- add MAX_NET_EDICTS and MAX_NET_EDICTS_MASK defines, which are 512
and 511 respectively
- change baselines to access the array directly, rather than through
the entity's "data" field
- cleanup SV_ReliableSVC_Emit
- add entity remapping. the entity number used internally in the
server no longer matches the number sent to the client, and it
releases the mapping after 10 seconds of inuse, so there's no
"512 entity limit" anymore. Still the MAX_EDICTS limit though,
which is currently 768, but it can probably be defined to something
much higher without any trouble.