git-push: allow -f as an alias for --force

This was already documented in the options section of the manpage. This
patch implements it, adds it to the usage message, and mentions it at the
top of the manpage.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <junkio@cox.net>

Documentation/git-push.txt

@@ -8,7 +8,7 @@ git-push - Update remote refs along with associated objects
 
 SYNOPSIS
 --------
-'git-push' [--all] [--tags] [--force] <repository> <refspec>...
+'git-push' [--all] [--tags] [-f | --force] <repository> <refspec>...
 
 DESCRIPTION
 -----------

builtin-push.c

@@ -8,7 +8,7 @@
 
 #define MAX_URI (16)
 
-static const char push_usage[] = "git push [--all] [--tags] [--force] <repository> [<refspec>...]";
+static const char push_usage[] = "git push [--all] [--tags] [-f | --force] <repository> [<refspec>...]";
 
 static int all = 0, tags = 0, force = 0, thin = 1;
 static const char *execute = NULL;
@@ -291,7 +291,7 @@ int cmd_push(int argc, const char **argv, const char *prefix)
 			tags = 1;
 			continue;
 		}
-		if (!strcmp(arg, "--force")) {
+		if (!strcmp(arg, "--force") || !strcmp(arg, "-f")) {
 			force = 1;
 			continue;
 		}