git: grok 'help' to mean '--help'.

Most other scm's understand it, most users expect it and it's an easy fix.
Signed-off-by: NAndreas Ericsson <ae@op5.se>
Signed-off-by: NJunio C Hamano <junkio@cox.net>

git.c

@@ -244,6 +244,11 @@ int main(int argc, char **argv, char **envp)
 	for (i = 1; i < argc; i++) {
 		char *arg = argv[i];
 
+		if (!strcmp(arg, "help")) {
+			show_help = 1;
+			continue;
+		}
+
 		if (strncmp(arg, "--", 2))
 			break;