fetch, remote: properly convey --no-prune options to subprocesses

If --no-prune is passed to one of the following commands:

    git fetch --all
    git fetch --multiple
    git fetch --recurse-submodules
    git remote update

then it must also be passed to the "fetch" subprocesses that those
commands use to do their work.  Otherwise there might be a fetch.prune
or remote.<name>.prune configuration setting that causes pruning to
occur, contrary to the user's express wish.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/fetch.c

@@ -936,8 +936,8 @@ static void add_options_to_argv(struct argv_array *argv)
 {
 	if (dry_run)
 		argv_array_push(argv, "--dry-run");
-	if (prune > 0)
-		argv_array_push(argv, "--prune");
+	if (prune != -1)
+		argv_array_push(argv, prune ? "--prune" : "--no-prune");
 	if (update_head_ok)
 		argv_array_push(argv, "--update-head-ok");
 	if (force)

builtin/remote.c

@@ -1371,7 +1371,7 @@ static int get_remote_default(const char *key, const char *value, void *priv)
 
 static int update(int argc, const char **argv)
 {
-	int i, prune = 0;
+	int i, prune = -1;
 	struct option options[] = {
 		OPT_BOOL('p', "prune", &prune,
 			 N_("prune remotes after fetching")),
@@ -1386,8 +1386,8 @@ static int update(int argc, const char **argv)
 
 	argv_array_push(&fetch_argv, "fetch");
 
-	if (prune)
-		argv_array_push(&fetch_argv, "--prune");
+	if (prune != -1)
+		argv_array_push(&fetch_argv, prune ? "--prune" : "--no-prune");
 	if (verbose)
 		argv_array_push(&fetch_argv, "-v");
 	argv_array_push(&fetch_argv, "--multiple");