chg: be stricter about checking invocation of `serve` command

Few tests run serve command in form of `hg -R <repo> serve` which leads to chg
thinking that it's not a serve command and failing tests.

We become more stricter in checking for the serve command.

This fixes test-server-view.t, test-remote-hidden.t, test-remotefilelog-http.t,
test-phases-exchange.t, test-wireproto-content-redirects.t with chg.

contrib/chg/chg.c

@@ -374,8 +374,7 b' static int runinstructions(struct cmdser'
 
 /*
  * Test whether the command is unsupported or not. This is not designed to
- * cover all cases. But it's fast, does not depend on the server and does
- * not return false positives.
+ * cover all cases. But it's fast, does not depend on the server.
  */
 static int isunsupported(int argc, const char *argv[])
 {
@@ -388,7 +387,12 b' static int isunsupported(int argc, const'
 	for (i = 0; i < argc; ++i) {
 		if (strcmp(argv[i], "--") == 0)
 			break;
-		if (i == 0 && strcmp("serve", argv[i]) == 0)
+		/*
+		 * there can be false positives but no false negative
+		 * we cannot assume `serve` will always be first argument
+		 * because global options can be passed before the command name
+		 */
+		if (strcmp("serve", argv[i]) == 0)
 			state |= SERVE;
 		else if (strcmp("-d", argv[i]) == 0 ||
 		         strcmp("--daemon", argv[i]) == 0)