maint: new syntax-check rule to ensure that AUTHORS stays in sync

* cfg.mk (sc_check_AUTHOR_list): New rule.
* .mailmap: New file, to tell git log how to map email addresses.

.mailmap

@@ -0,0 +1,12 @@
+<amy.griffis@hp.com> <aron.griffis@hp.com>
+<bozzolan@gmail.com> <redshift@gmx.com>
+<charles_duffy@messageone.com> <charles@dyfis.net>
+<dfj@redhat.com> <dfj@dfj.bne.redhat.com>
+<eblake@redhat.com> <ebb9@byu.net>
+<gdolley@arpnetworks.com> <gdolley@ucla.edu>
+<gerhard.stenzel@de.ibm.com> <gstenzel@linux.vnet.ibm.com>
+<jamie@canonical.com> <jamie@ubuntu.com>
+<laine@redhat.com> <laine@laine.org>
+<meyering@redhat.com> <jim@meyering.net>
+<socketpair@gmail.com> <socketpair gmail com>
+<soren@canonical.com> <soren@ubuntu.com>

cfg.mk

@@ -472,6 +472,20 @@ Makefile: _autogen
   endif
 endif
 
+# Give credit where due:
+# Ensure that each commit author email address (possibly mapped via
+# git log's .mailmap) appears in our AUTHORS file.
+sc_check_author_list:
+	@fail=0;							\
+	for i in $$(git log --pretty=format:%aE%n|sort -u|grep -v '^$$'); do \
+	  sanitized=$$(echo "$$i"|LC_ALL=C sed 's/\([^a-zA-Z0-9_@-]\)/\\\1/g'); \
+	  grep -iq "<$$sanitized>" AUTHORS				\
+	    || { printf '%s\n' "$$i" >&2; fail=1; };			\
+	done;								\
+	test $$fail = 1							\
+	  && echo '$(ME): committer(s) not listed in AUTHORS' >&2;	\
+	test $$fail = 0
+
 # It is necessary to call autogen any time gnulib changes.  Autogen
 # reruns configure, then we regenerate all Makefiles at once.
 .PHONY: _autogen