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.

6 files changed, 8 insertions, 8 deletions

diff --git a/maintainer/am-ft b/maintainer/am-ft
index 6bb7d97e5..48eb5ba54 100755
--- a/maintainer/am-ft
+++ b/maintainer/am-ft
@@ -15,7 +15,7 @@
 # GNU General Public License for more details.
 
 # You should have received a copy of the GNU General Public License
-# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
 # TODO: some documentation would be nice ...
 
diff --git a/maintainer/am-xft b/maintainer/am-xft
index 98263babb..958a21a96 100755
--- a/maintainer/am-xft
+++ b/maintainer/am-xft
@@ -12,7 +12,7 @@
 # GNU General Public License for more details.
 
 # You should have received a copy of the GNU General Public License
-# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
 MAKE=${MAKE-make} GIT=${GIT-git}
 $GIT clean -fdx && $MAKE bootstrap && $MAKE dist && exec am-ft "$@"
diff --git a/maintainer/check-perl-protos b/maintainer/check-perl-protos
index b1d6a72b5..649aafb34 100755
--- a/maintainer/check-perl-protos
+++ b/maintainer/check-perl-protos
@@ -13,7 +13,7 @@
 # GNU General Public License for more details.
 #
 # You should have received a copy of the GNU General Public License
-# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
 use warnings;
 use strict;
diff --git a/maintainer/maint.mk b/maintainer/maint.mk
index 1cfd2e870..51907193c 100644
--- a/maintainer/maint.mk
+++ b/maintainer/maint.mk
@@ -13,7 +13,7 @@
 # GNU General Public License for more details.
 #
 # You should have received a copy of the GNU General Public License
-# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
 # Avoid CDPATH issues.
 unexport CDPATH
@@ -286,7 +286,7 @@ announcement: NEWS
 	$(AM_V_GEN): \
 	  && rm -f $@ $@-t \
 	  && $(determine_release_type) \
-	  && ftp_base="ftp://$$dest.gnu.org/gnu/$(PACKAGE)" \
+	  && ftp_base="https://$$dest.gnu.org/gnu/$(PACKAGE)" \
 	  && X () { printf '%s\n' "$$*" >> $@-t; } \
 	  && X "We are pleased to announce the $(PACKAGE_NAME) $(VERSION)" \
 	       "$$announcement_type." \
@@ -502,7 +502,7 @@ update-copyright:
 #  Run the testsuite with the least supported autoconf version.  #
 # -------------------------------------------------------------- #
 
-gnu-ftp = http://ftp.gnu.org/gnu
+gnu-ftp = https://ftp.gnu.org/gnu
 
 # Various shorthands: version, name, package name, tarball name,
 # tarball location, installation directory.
diff --git a/maintainer/rename-tests b/maintainer/rename-tests
index 8c643872b..b933016f3 100755
--- a/maintainer/rename-tests
+++ b/maintainer/rename-tests
@@ -14,7 +14,7 @@
 # GNU General Public License for more details.
 
 # You should have received a copy of the GNU General Public License
-# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
 set -e -u
 
diff --git a/maintainer/syntax-checks.mk b/maintainer/syntax-checks.mk
index 699203ad8..7223eca6b 100644
--- a/maintainer/syntax-checks.mk
+++ b/maintainer/syntax-checks.mk
@@ -13,7 +13,7 @@
 # GNU General Public License for more details.
 #
 # You should have received a copy of the GNU General Public License
-# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
 # We also have to take into account VPATH builds (where some generated
 # tests might be in '$(builddir)' rather than in '$(srcdir)'), TAP-based