rebase: add --reset-author-date

The previous commit introduced --ignore-date flag to interactive
rebase, but the name is actually very vague in context of rebase -i
since there are two dates we can work with. Add an alias to convey
the precise purpose.

Signed-off-by: Rohit Ashiwal <rohit.ashiwal265@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-rebase.txt

@@ -391,6 +391,7 @@ See also INCOMPATIBLE OPTIONS below.
 	as the committer date. This implies --force-rebase.
 
 --ignore-date::
+--reset-author-date::
 	Instead of using the given author date, reset it to the
 	current time. This implies --force-rebase.
 +

builtin/rebase.c

@@ -1436,6 +1436,8 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		OPT_BOOL(0, "committer-date-is-author-date",
 			 &options.committer_date_is_author_date,
 			 N_("make committer date match author date")),
+		OPT_BOOL(0, "reset-author-date", &options.ignore_date,
+			 "ignore author date and use current date"),
 		OPT_BOOL(0, "ignore-date", &options.ignore_date,
 			 "ignore author date and use current date"),
 		OPT_PASSTHRU_ARGV('C', NULL, &options.git_am_opts, N_("n"),