netlib Cleanup

When the network library is no longer required (as of the first free source drop, netlib is always required and cannot be broken out as a separate component), a call is made to NET_ShutdownNetLib() to cleanup anything netlib may have done.

Cleanup consists of aborting any urls waiting for load completion, destroying/freeing any memory allocated (including the memory cache), closing the global history database, and writing the cookies in memory to disk.

Judson Valeski, 1998