All my changes in source code I marked with comments starting with -JL-.

Changes against original glBSP version 1.91:

* Fixed bug, that caused pruning of all sidedefs in Hexen maps.

* Removed old polyobj handling that caused polyobjs not to work at all.

* Added corect polyobj handling. Now it will find all polyobj sectors and
 will never split them.

* Hexen mode is identified by the presence of BEHAVIOR lump, command line
 option -hexen is not recognized anymore.

* Recognizes SCRIPTS lump with script sources.

* Recognizes GL_PVS lump, will add empty GL_PVS lump.
