do not discard const: the ugly truth

ISOC23 reveals that we mutate argv strings in place. Confess to this
with explicit casts.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: mjg

builtin/rev-parse.c

@@ -265,7 +265,7 @@ static int show_file(const char *arg, int output_prefix)
 	return 0;
 }
 
-static int try_difference(const char *arg)
+static int try_difference(char *arg)
 {
 	char *dotdot;
 	struct object_id start_oid;
@@ -325,7 +325,7 @@ static int try_difference(const char *arg)
 	return 0;
 }
 
-static int try_parent_shorthands(const char *arg)
+static int try_parent_shorthands(char *arg)
 {
 	char *dotdot;
 	struct object_id oid;
@@ -1145,9 +1145,9 @@ int cmd_rev_parse(int argc,
 		}
 
 		/* Not a flag argument */
-		if (try_difference(arg))
+		if (try_difference((char *) arg))
 			continue;
-		if (try_parent_shorthands(arg))
+		if (try_parent_shorthands((char *) arg))
 			continue;
 		name = arg;
 		type = NORMAL;

revision.c

@@ -2132,7 +2132,7 @@ static int handle_dotdot(const char *arg,
 			 int cant_be_filename)
 {
 	struct object_context a_oc = {0}, b_oc = {0};
-	char *dotdot = strstr(arg, "..");
+	char *dotdot = (char *) strstr(arg, "..");
 	int ret;
 
 	if (!dotdot)
@@ -2176,7 +2176,7 @@ static int handle_revision_arg_1(const char *arg_, struct rev_info *revs, int fl
 		goto out;
 	}
 
-	mark = strstr(arg, "^@");
+	mark = (char *) strstr(arg, "^@");
 	if (mark && !mark[2]) {
 		*mark = 0;
 		if (add_parents_only(revs, arg, flags, 0)) {
@@ -2185,13 +2185,13 @@ static int handle_revision_arg_1(const char *arg_, struct rev_info *revs, int fl
 		}
 		*mark = '^';
 	}
-	mark = strstr(arg, "^!");
+	mark = (char *) strstr(arg, "^!");
 	if (mark && !mark[2]) {
 		*mark = 0;
 		if (!add_parents_only(revs, arg, flags ^ (UNINTERESTING | BOTTOM), 0))
 			*mark = '^';
 	}
-	mark = strstr(arg, "^-");
+	mark = (char *) strstr(arg, "^-");
 	if (mark) {
 		int exclude_parent = 1;