Modified the way booleans preserve face data, and cleaned up some

Modified the way booleans preserve face data, and cleaned up some
duplicate code. Also removed redundant files from the bsp module,
that where replaced by boolop last year, no sense in updating them
for these changes. On the user level things should still work the
same, this is only preparation work.

Not counting the removed files, -1501 lines of code, not too bad :)