chg: limit reconnect attempts

Some users may have hg as a wrapper script which sets sensitive environment
variables (like setting up virtualenv). This will make chg redirect forever
because the environment variables are never considered up to date.
This patch adds a limit (10) for reconnect attempts and warn the user with
a possible solution if the limit is exceeded.

contrib/chg/chg.c

@@ -549,6 +549,7 b' int main(int argc, const char *argv[], c'
 	}
 
 	hgclient_t *hgc;
+	size_t retry = 0;
 	while (1) {
 		hgc = connectcmdserver(&opts);
 		if (!hgc)
@@ -560,6 +561,13 b' int main(int argc, const char *argv[], c'
 		runinstructions(&opts, insts);
 		free(insts);
 		hgc_close(hgc);
+		if (++retry > 10)
+			abortmsg("too many redirections.\n"
+				 "Please make sure %s is not a wrapper which "
+				 "changes sensitive environment variables "
+				 "before executing hg. If you have to use a "
+				 "wrapper, wrap chg instead of hg.",
+				 gethgcmd());
 	}
 
 	setupsignalhandler(hgc_peerpid(hgc));