client and server: Some fixes with userinfo in engine.

Merge ioquake/ioq3@86c41d39daee32393d5d48f7fe099bbfd18b0fa7 (Fix sending reliable commands before being connected, patch by Eugene C.)
Stop eating userinfo cmd in client.  With the source open, it serves little purpose leaving it there.
Prevent users executing userinfo cmd with no arguments.
Use Com_sprintf in SV_CheckClientUserinfoTimer.