Doomsday Engine

WAD module version 3

• Implementation uses the OO paradigm.
• Lump cache implemented at file level rather than lump directory level;
  means we no longer have to worry about updating Zone user pointers or
  resizing the cache pointer table when a new WAD is opened/closed.
• Lump directory independence from the wad file list;
  means any number of lump directories can coexist in parallel and
  they can be (re)built without touching the file list.
• Deferred lump cache allocation; means if caching isn't used on lumps
  of a particular WAD file, we don't waste memory allocating the cache
  pointer table.

Note that the net protocol version was incremented (breaking compatibility)
as it is nolonger necessary to communicate the file name of the iwad in
server_info_t. This is because the combination of game identity-key and
iwad CRC will cover all eventualities.