Teach --[no-]rerere-autoupdate option to merge, revert and friends

Introduce a command line option to override rerere.autoupdate configuration
variable to make it more useful.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/parse-options.h b/parse-options.h
index f295a2c..91c1500 100644
--- a/parse-options.h
+++ b/parse-options.h
@@ -123,6 +123,8 @@
 				      (h), PARSE_OPT_NOARG, NULL, (p) }
 #define OPT_INTEGER(s, l, v, h)     { OPTION_INTEGER, (s), (l), (v), "n", (h) }
 #define OPT_STRING(s, l, v, a, h)   { OPTION_STRING,  (s), (l), (v), (a), (h) }
+#define OPT_UYN(s, l, v, h)         { OPTION_CALLBACK, (s), (l), (v), NULL, \
+				      (h), PARSE_OPT_NOARG, &parse_opt_tertiary }
 #define OPT_DATE(s, l, v, h) \
 	{ OPTION_CALLBACK, (s), (l), (v), "time",(h), 0, \
 	  parse_opt_approxidate_cb }
@@ -190,6 +192,7 @@
 extern int parse_opt_approxidate_cb(const struct option *, const char *, int);
 extern int parse_opt_verbosity_cb(const struct option *, const char *, int);
 extern int parse_opt_with_commit(const struct option *, const char *, int);
+extern int parse_opt_tertiary(const struct option *, const char *, int);
 
 #define OPT__VERBOSE(var)  OPT_BOOLEAN('v', "verbose", (var), "be verbose")
 #define OPT__QUIET(var)    OPT_BOOLEAN('q', "quiet",   (var), "be quiet")