Prefer https: URLs

In Gnulib, Emacs, etc. we are changing ftp: and http: URLs to use
https:, to discourage man-in-the-middle attacks when downloading
software. The attached patch propagates these changes upstream to
Automake.  This patch does not affect files that Automake is
downstream of, which I'll patch separately.

Althouth the resources are not secret, plain HTTP is vulnerable to
malicious routers that tamper with responses from GNU servers,
and this sort of thing is all too common when people in some other
countries browse US-based websites. See, for example:

Aceto G, Botta A, Pescapé A, Awan MF, Ahmad T, Qaisar
S. Analyzing internet censorship in Pakistan. RTSI
2016. https://dx.doi.org/10.1109/RTSI.2016.7740626

HTTPS is not a complete solution here, but it can be a significant
help. The GNU project regularly serves up code to users, so we should
take some care here.

3 files changed, 12 insertions, 12 deletions

diff --git a/PLANS/obsolete-removed/am-prog-mkdir-p.txt b/PLANS/obsolete-removed/am-prog-mkdir-p.txt
index 20d5cf52c..c18f94571 100644
--- a/PLANS/obsolete-removed/am-prog-mkdir-p.txt
+++ b/PLANS/obsolete-removed/am-prog-mkdir-p.txt
@@ -8,14 +8,14 @@ Automake 1.13 -- see commit 'v1.12-20-g8a1c64f'.
 Alas, it turned out the latest Gettext version at the time (0.18.1.1) was
 still using that macro:
 
-  <http://lists.gnu.org/archive/html/automake/2012-09/msg00010.html>
+  <https://lists.gnu.org/archive/html/automake/2012-09/msg00010.html>
 
 And since the maintenance of Gettext was stalled, I couldn't get a fix
 committed and released in time for the appearance of Automake 1.13:
 
-  <http://lists.gnu.org/archive/html/bug-gettext/2012-04/msg00018.html>
-  <http://lists.gnu.org/archive/html/bug-gettext/2012-06/msg00012.html>
-  <http://lists.gnu.org/archive/html/bug-gettext/2012-10/msg00001.html>
+  <https://lists.gnu.org/archive/html/bug-gettext/2012-04/msg00018.html>
+  <https://lists.gnu.org/archive/html/bug-gettext/2012-06/msg00012.html>
+  <https://lists.gnu.org/archive/html/bug-gettext/2012-10/msg00001.html>
 
 So, on strong advice by Jim Meyering, in commit 'v1.12.4-158-gdf23daf'
 I re-introduced AM_PROG_MKDIR_P in Automake (thanks to Jim for having
@@ -41,7 +41,7 @@ calls), and of course, the pre-0.18.2 version of some of these files
 still contains occurrences of AM_PROG_MKDIR_P -- so Automake 1.13 errors
 out, and we lose.  That already happened in practice:
 
-    <http://lists.gnu.org/archive/html/bug-grep/2013-01/msg00003.html>
+    <https://lists.gnu.org/archive/html/bug-grep/2013-01/msg00003.html>
 
 Moreover, while I might see it as not unreasonable to ask a developer
 using Automake 2.0 to also update Gettext to 1.18.2, that would not
diff --git a/PLANS/subdir-objects.txt b/PLANS/subdir-objects.txt
index c849e338e..c6a046f52 100644
--- a/PLANS/subdir-objects.txt
+++ b/PLANS/subdir-objects.txt
@@ -3,7 +3,7 @@ Summary
 
 We want to make the behaviour currently enabled by the 'subdir-objects'
 the default one, and in fact the *only* one, in Automake 2.0.
-See automake bug#13378: <http://debbugs.gnu.org/13378>.
+See automake bug#13378: <https://debbugs.gnu.org/13378>.
 
 Details
 -------
@@ -29,8 +29,8 @@ DONE for automake 1.13.2
 
 The bug spotted by Nick Bowler:
 
-  <http://debbugs.gnu.org/cgi/bugreport.cgi?bug=13378#35>
-  <http://debbugs.gnu.org/cgi/bugreport.cgi?bug=13378#44>
+  <https://debbugs.gnu.org/cgi/bugreport.cgi?bug=13378#35>
+  <https://debbugs.gnu.org/cgi/bugreport.cgi?bug=13378#44>
 
 and exposed in test case 't/ccnoco4.sh' has been fixed (see commit
 v1.13.1-56-g34001a9).  The bug was due to the fact that Automake-generated
@@ -53,7 +53,7 @@ for suggesting this).
 For automake 1.16 (*before* 2.0 can be released)
 ------------------------------------------------
 
-Submit the pending patch series that fixes http://debbugs.gnu.org/13928
+Submit the pending patch series that fixes https://debbugs.gnu.org/13928
 
 For automake 2.0
 ----------------
diff --git a/PLANS/texi/drop-split-info-files.txt b/PLANS/texi/drop-split-info-files.txt
index a0a5636e7..f13a32419 100644
--- a/PLANS/texi/drop-split-info-files.txt
+++ b/PLANS/texi/drop-split-info-files.txt
@@ -2,12 +2,12 @@ For in Automake 2.0 (DONE)
 --------------------------
 
 We will drop split info files in Automake 2.0.
-See automake bug#13351: <http://debbugs.gnu.org/13351>.
+See automake bug#13351: <https://debbugs.gnu.org/13351>.
 
 Basically, it has been confirmed that the original reason behind
 the existence of split info files was indeed "efficiency,
 especially memory size":
-<http://lists.gnu.org/archive/html/texinfo-devel/2012-08/msg00024.html>
+<https://lists.gnu.org/archive/html/texinfo-devel/2012-08/msg00024.html>
 
 So split info files have lost their reason d'etre on modern systems
 (where even Emacs has become a lightweight program ;-).  And you are
@@ -16,7 +16,7 @@ not using an embedded system to read Info documentation, right?
 In addition, it appears that the use of split info files (at least
 the way Automake-generated rules have been handling them for a long
 time) can cause real problems in some (admittedly quite corner-case)
-situations; see automake bug#12320: <http://debbugs.gnu.org/12320>.
+situations; see automake bug#12320: <https://debbugs.gnu.org/12320>.
 
 This change should be completely transparent to the developer (no
 adjustments needed to be made to Makefile.am or other parts of the