Only save modified texture definition lumps.

Don't overwrite unmodified texture definition lumps since people might
want to preserve TEXTURES comments.
Removed a bunch of wxWidgets 2.9.x baggage.

Some of which were broken when using wxWidgets 3.0.0 because suddenly
wxMINOR_VERSION and wxRELEASE_NUMBER were no longer greater than
whatever value was tested.
ZDoom mapinfo fix