Nothing was pointing at BBGE/glext.
Only the VS project was pointing at ExternalLibs/GL. I have pointed it
at the headers under BBGE/GL instead.
I have also adjusted the includes to use the GL prefix as is standard
practise. These will still work as BBGE is in the include path. This
allows users to build against their system GL headers simply by
deleting the BBGE/GL directory.
- fixed warning about PlaySfx::handle
- fixed displaying subtitles - if the path was not full lowercase it didn't find its txt files.
- CMake: removed SDLMAIN_FOUND, which is seemingly only defined on windows and does more harm than good.
- glpng: always use new libpng API (fixes windows build)