Use ulimit to Set Queue Size

[technojoe]

NOTE: This change needs testing.
 
Summary: Use returned value from getrlimit to dynamically allocate memory for client_cs, which removes the hardcoded, arbitrary limit of 1000. In effect, the ulimit for file descriptors becomes the maximum queue size, and ulimit is a system-configurable value.

Details:

1. Changed "client_cs" from a global array to a global pointer, which allows malloc to be used later.
2. Set "max" to an initial value of 1000, which is only used if getrlimit fails to return a value.
3. Moved the getrlimit section to earlier within get_max_descriptors, so its return value could be used as a starting point.
4. Added malloc for "client_cs" in server_main immediately after get_max_descriptors returns.
5. Added free for "client_cs" in end_server.
6. Removed enum MAXCONN, since it is no longer needed.

[justanhduc]

Thanks @technojoe!