[man pages]: Define page-local `MR` fallback.

[man pages]: Provide page-local fallback definition of new `MR` macro.
I didn't think I was going to have to do this, but the premier site on
the web for viewing Linux man pages, Michael Kerrisk's man7.org, has
been pulling snapshots of the pages themselves without upgrading the
underlying macros, and so man page cross references set with `MR` are
getting lost in its presentations.  (I acknowledge: Ingo Schwarze warned
me something like this could happen.)  This definition is intended as a
stopgap measure only.  I want to revert this after groff 1.23 is
released and has spread to some reasonable degree.

* contrib/chem/chem.1.man:
* contrib/eqn2graph/eqn2graph.1.man:
* contrib/gdiffmk/gdiffmk.1.man:
* contrib/glilypond/glilypond.1.man:
* contrib/gperl/gperl.1.man:
* contrib/gpinyin/gpinyin.1.man:
* contrib/grap2graph/grap2graph.1.man:
* contrib/hdtbl/groff_hdtbl.7.man:
* contrib/mm/groff_mm.7.man:
* contrib/mm/groff_mmse.7.man:
* contrib/mm/mmroff.1.man:
* contrib/mom/groff_mom.7.man:
* contrib/pdfmark/pdfroff.1.man:
* contrib/pic2graph/pic2graph.1.man:
* contrib/rfc1345/groff_rfc1345.7.man:
* man/groff.7.man:
* man/groff_char.7.man:
* man/groff_diff.7.man:
* man/groff_font.5.man:
* man/groff_out.5.man:
* man/groff_tmac.5.man:
* man/roff.7.man:
* src/devices/grodvi/grodvi.1.man:
* src/devices/grohtml/grohtml.1.man:
* src/devices/grolbp/grolbp.1.man:
* src/devices/grolj4/grolj4.1.man:
* src/devices/gropdf/gropdf.1.man:
* src/devices/gropdf/pdfmom.1.man:
* src/devices/grops/grops.1.man:
* src/devices/grotty/grotty.1.man:
* src/devices/xditview/gxditview.1.man:
* src/preproc/eqn/eqn.1.man:
* src/preproc/eqn/neqn.1.man:
* src/preproc/grn/grn.1.man:
* src/preproc/pic/pic.1.man:
* src/preproc/preconv/preconv.1.man:
* src/preproc/refer/refer.1.man:
* src/preproc/soelim/soelim.1.man:
* src/preproc/tbl/tbl.1.man:
* src/roff/groff/groff.1.man:
* src/roff/nroff/nroff.1.man:
* src/roff/troff/troff.1.man:
* src/utils/addftinfo/addftinfo.1.man:
* src/utils/afmtodit/afmtodit.1.man:
* src/utils/grog/grog.1.man:
* src/utils/hpftodit/hpftodit.1.man:
* src/utils/indxbib/indxbib.1.man:
* src/utils/lkbib/lkbib.1.man:
* src/utils/lookbib/lookbib.1.man:
* src/utils/pfbtops/pfbtops.1.man:
* src/utils/tfmtodit/tfmtodit.1.man:
* src/utils/xtotroff/xtotroff.1.man:
* tmac/groff_man.7.man.in:
* tmac/groff_me.7.man:
* tmac/groff_ms.7.man:
* tmac/groff_trace.7.man:
* tmac/groff_www.7.man: Do it.

Fixes <https://savannah.gnu.org/bugs/?63825>.  Thanks greatly to Alexis
for identifying an issue with mandoc(1)'s handling of an earlier
iteration of this fallback, and to John Gardner for identifying a method
of detecting mandoc as the renderer at formatting time.

Tested with groff 1.22.4, mandoc 1.14.5, and groff Git HEAD (of course).

The sed script I used follows.

/^\.cp 0/a\
.\
.\\" Define fallback for groff 1.23's MR macro if the system lacks it.\
.nr do-fallback 0\
.if !\\n(.f           .nr do-fallback 1 \\" mandoc\
.if  \\n(.g .if !d MR .nr do-fallback 1 \\" older groff\
.if !\\n(.g           .nr do-fallback 1 \\" non-groff *roff\
.if \\n[do-fallback]  \\{\\\
.  de MR\
.    ie \\\\n(.$=1 \\\
.      I \\%\\\\$1\
.    el \\\
.      IR \\%\\\\$1 (\\\\$2)\\\\$3\
.  .\
.\\}\
.rr do-fallback

ANNOUNCE: Update bug counts.  Credit Alexis with assistance.

1 files changed, 4 insertions, 3 deletions

diff --git a/ANNOUNCE b/ANNOUNCE
index d9bd26c4f..31cf029a9 100644
--- a/ANNOUNCE
+++ b/ANNOUNCE
@@ -54,7 +54,7 @@ release shipped with three automated unit tests; this one ships with
 over 160 unit and regression tests.
 
 As of this writing, per the GNU Savannah bug tracker, the groff project
-has resolved 416 problems as fixed for the 1.23.0 release.  Some of the
+has resolved 417 problems as fixed for the 1.23.0 release.  Some of the
 bugs we've corrected were over 30 years old.
 
 Classifying these issues by type and the component of the project to
@@ -64,14 +64,14 @@ which they apply, we find the following.
   ----                              ---------
   Build/installation           39   Core                           96
   Crash/unresponsive           11   Driver: grohtml                 7
-  Documentation               101   Driver: gropdf                  9
+  Documentation               102   Driver: gropdf                  9
   Feature change               40   Driver: grops                   2
   Incorrect behavior          129   Driver: grotty                  4
   Lint                         15   Driver: others/general          8
   Rendering/cosmetics          10   Font: devpdf                    1
   Test                          4   Font: devps                     3
   Warning/suspicious behavior  67   Font: others/general            4
-                                    General                        47
+                                    General                        48
                                     Macros: man                    33
                                     Macros: mdoc                   13
                                     Macros: me                     36
@@ -159,6 +159,7 @@ of this release.
 Alan D. Salewski
 Alex Colomar
 Alexander Kanavin
+Alexis
 Andreas Kusalananda Kähäri
 Axel Kielhorn
 Ben Wong