Remove unnecessary usage of strncmp() in git-rev-list arg parsing.

Not only is it unnecessary, it incorrectly allows extraneous characters
at the end of the argument.

Junio noticed the --merge-order thing, and Jon points out that if we fix
that one, we should fix --show-breaks too.

rev-list.c

@@ -462,11 +462,11 @@ int main(int argc, char **argv)
 			limited = 1;
 			continue;
 		}
-		if (!strncmp(arg, "--merge-order", 13)) {
+		if (!strcmp(arg, "--merge-order")) {
 		        merge_order = 1;
 			continue;
 		}
-		if (!strncmp(arg, "--show-breaks", 13)) {
+		if (!strcmp(arg, "--show-breaks")) {
 			show_breaks = 1;
 			continue;
 		}