pass 1 on serverside demo recording.

each client_t now has a demoInfo_t struct maintaining the demo recording
state for that client.  demo recording is triggered the same way as through
the client (\record demoname, \stoprecord), and the client to record is
picked to be the first active client not already being recorded if not
explicitly specified.
Merge pull request #480 from dpadgett/svdemo

pass 1 on serverside demo recording.