fast-import: tighten parsing of boolean command line options

We parse options like "--max-pack-size=" using skip_prefix(), which
makes sense to get at the bytes after the "=". However, we also parse
"--quiet" and "--stats" with skip_prefix(), which allows things like
"--quiet-nonsense" to behave like "--quiet".

This was a mistaken conversion in 0f6927c229 (fast-import: put option
parsing code in separate functions, 2009-12-04). Let's tighten this to
an exact match, which was the original intent.

Signed-off-by: Jeff King <peff@peff.net>

fast-import.c

@@ -3312,9 +3312,9 @@ static int parse_one_option(const char *option)
 		option_active_branches(option);
 	} else if (skip_prefix(option, "export-pack-edges=", &option)) {
 		option_export_pack_edges(option);
-	} else if (starts_with(option, "quiet")) {
+	} else if (!strcmp(option, "quiet")) {
 		show_stats = 0;
-	} else if (starts_with(option, "stats")) {
+	} else if (!strcmp(option, "stats")) {
 		show_stats = 1;
 	} else {
 		return 0;