Fix 'commit-msg' to cite 'CONTRIBUTE'

As suggested in:
http://lists.gnu.org/archive/html/emacs-devel/2015-03/msg00947.html
Also, have the two files match better.
* CONTRIBUTE: Match what's in build-aux/git-hooks/commit-msg.
* build-aux/git-hooks/commit-msg: Mention 'CONTRIBUTE'.

CONTRIBUTE

@@ -37,16 +37,17 @@ specify the actual author; the committer defaults to you.
 When using git, commit messages should use ChangeLog format, with the
 following modifications:
 
-- Add a single short line explaining the change, then an empty line,
-  then unindented ChangeLog entries.
+- Start with a single unindented summary line explaining the change,
+  then an empty line, then unindented ChangeLog entries.
 
   You can use various Emacs functions to ease this process; see (info
   "(emacs)Change Log Commands") or
   http://www.gnu.org/software/emacs/manual/html_node/emacs/Change-Log-Commands.html.
 
-- The summary line is limited to 72 characters (enforced by a commit
-  hook). If you have trouble making that a good summary, add a
-  paragraph below it, before the individual file descriptions.
+- Limit lines in commit messages to 78 characters, unless they consist
+  of a single word of at most 140 characters.  If you have trouble
+  fitting the summary into 78 characters, add a summarizing paragraph
+  below the empty line and before the individual file descriptions.
 
 - If only a single file is changed, the summary line can be the normal
   file first line (starting with the asterisk).  Then there is no
@@ -57,6 +58,11 @@ following modifications:
   the rationale for a change; that can be done in the commit message
   between the summary line and the file entries.
 
+- Commit messages should contain only printable UTF-8 characters.
+
+- Commit messages should not contained the "Signed-off-by:" lines that
+  are used in some other projects.
+
 ** ChangeLog notes
 
 - Emacs generally follows the GNU coding standards when it comes to

ChangeLog

@@ -1,3 +1,12 @@
+2015-03-29  Paul Eggert  <eggert@cs.ucla.edu>
+
+	Fix 'commit-msg' to cite 'CONTRIBUTE'
+	As suggested in:
+	http://lists.gnu.org/archive/html/emacs-devel/2015-03/msg00947.html
+	Also, have the two files match better.
+	* CONTRIBUTE: Match what's in build-aux/git-hooks/commit-msg.
+	* build-aux/git-hooks/commit-msg: Mention 'CONTRIBUTE'.
+
 2015-03-23  Andreas Schwab  <schwab@suse.de>
 
 	* configure.ac: Fix jpeg version check to work with gcc >= 5.

build-aux/git-hooks/commit-msg

@@ -63,7 +63,7 @@ exec $awk '
   /^#/ { next }
 
   !/^.*$/ {
-    print "Invalid character (not UTF-8) in commit message"
+    print "Invalid character (not UTF-8) in commit message; see 'CONTRIBUTE'"
     status = 1
   }
 
@@ -77,13 +77,13 @@ exec $awk '
       sub(/^squash! /, "")
 
     if ($0 ~ "^" space) {
-      print "White space at start of commit message'\''s first line"
+      print "White space at start of commit message'\''s first line; see 'CONTRIBUTE'"
       status = 1
     }
   }
 
   nlines == 2 && $0 ~ non_space {
-    print "Nonempty second line in commit message"
+    print "Nonempty second line in commit message; see 'CONTRIBUTE'"
     status = 1
   }
 
@@ -97,28 +97,28 @@ exec $awk '
   }
 
   78 < length && $0 ~ space {
-    print "Line longer than 78 characters in commit message"
+    print "Line longer than 78 characters in commit message; see 'CONTRIBUTE'"
     status = 1
   }
 
   140 < length {
-    print "Word longer than 140 characters in commit message"
+    print "Word longer than 140 characters in commit message; see 'CONTRIBUTE'"
     status = 1
   }
 
   /^Signed-off-by: / {
-    print "'\''Signed-off-by:'\'' in commit message"
+    print "'\''Signed-off-by:'\'' in commit message; see 'CONTRIBUTE'"
     status = 1
   }
 
   $0 ~ non_print {
-    print "Unprintable character in commit message"
+    print "Unprintable character in commit message; see 'CONTRIBUTE'"
     status = 1
   }
 
   END {
     if (nlines == 0) {
-      print "Empty commit message"
+      print "Empty commit message; see 'CONTRIBUTE'"
       status = 1
     }
     exit status