stash: use named constant when parsing "--all"

The code that stashes all untracked files compares the value of the
"include_untracked" variable to the constant "INCLUDE_ALL_FILES",
however the option parsing code for "--all" uses a hard coded integer
instead. Replace the integer with the named constant.

Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/stash.c

diff --git a/builtin/stash.c b/builtin/stash.c
index c4809f2..b19ebd6 100644
--- a/builtin/stash.c
+++ b/builtin/stash.c
@@ -1929,7 +1929,7 @@ static int push_stash(int argc, const char **argv, const char *prefix,
 		OPT_BOOL('u', "include-untracked", &include_untracked,
 			 N_("include untracked files in stash")),
 		OPT_SET_INT('a', "all", &include_untracked,
-			    N_("include ignore files"), 2),
+			    N_("include ignore files"), INCLUDE_ALL_FILES),
 		OPT_STRING('m', "message", &stash_msg, N_("message"),
 			   N_("stash message")),
 		OPT_PATHSPEC_FROM_FILE(&pathspec_from_file),
@@ -2036,7 +2036,7 @@ static int save_stash(int argc, const char **argv, const char *prefix,
 		OPT_BOOL('u', "include-untracked", &include_untracked,
 			 N_("include untracked files in stash")),
 		OPT_SET_INT('a', "all", &include_untracked,
-			    N_("include ignore files"), 2),
+			    N_("include ignore files"), INCLUDE_ALL_FILES),
 		OPT_STRING('m', "message", &stash_msg, "message",
 			   N_("stash message")),
 		OPT_END()