Full ability to browse file directory tree from the runtime wad loader.

git-svn-id: http://mancubus.net/svn/hosted/eternity/trunk@2781 86ba831e-150c-0410-ab35-e06eaae15ed9
"NSG" style lookups must be sensitive to source loading order of lumps; otherwise, the "namespace first" semantics of an NSG lookup end up overriding the more important file loading order semantics of the WadDirectory.

git-svn-id: http://mancubus.net/svn/hosted/eternity/trunk@2782 86ba831e-150c-0410-ab35-e06eaae15ed9
Restore ability to play internal demos through -playdemo which was accidentally lost during refactoring of WadDirectory for zip file support.

git-svn-id: http://mancubus.net/svn/hosted/eternity/trunk@2783 86ba831e-150c-0410-ab35-e06eaae15ed9