Prevent setsid() failure from taking down ycmd
Only adjust updatetime if above 2000.

Goal is to lower it so don't raise it if already low.

Closes #834
Merge pull request #932 from RedBeard0531/master

Only adjust updatetime if above 2000.
Client/server communication now uses HMAC for auth

This is to prevent a convoluted exploit that can trigger remote code execution.
Error handler now also sets HMAC header.
Merge remote-tracking branch 'origin/master'