Merge branch 'jn/gc-auto'

"gc --auto" ended up calling exit(-1) upon error, which has been
corrected to use exit(1).  Also the error reporting behaviour when
daemonized has been updated to exit with zero status when stopping
due to a previously discovered error (which implies there is no
point running gc to improve the situation); we used to exit with
failure in such a case.

* jn/gc-auto:
  gc: do not return error for prior errors in daemonized mode

Documentation/config.txt

@@ -1643,7 +1643,8 @@ gc.writeCommitGraph::
 	for details.
 
 gc.logExpiry::
-	If the file gc.log exists, then `git gc --auto` won't run
+	If the file gc.log exists, then `git gc --auto` will print
+	its content and exit with status zero instead of running
 	unless that file is more than 'gc.logExpiry' old.  Default is
 	"1.day".  See `gc.pruneExpire` for more ways to specify its
 	value.