Since this is a non-standard function it's better kept to as few places as possible, so now DirEntryExists returns an additional flag to say what type an entry is and is being used nearly everywhere where stat was used, excluding a few low level parts in the POSIX code.
- moved timer definitions into their own header/source files. d_main is not the right place for this.
- removed some leftover cruft from the old timer code.
Most of those which still rely on ZDoom's own definition should be gone, unfortunately the code in files that include Windows headers is a gigantic mess with DWORDs being longs there intead of ints, so this needs to be done with care. DWORD should only remain where the Windows type is actually wanted.
- Replaced GTK/OS X (note different from Cocoa) clipboard code with SDL clipboard API.
- Removed requirement to link to GTK in order to compile with GTK support.
- GTK is no longer init'd if the GTK IWAD picker is not used.
- Our usage of GTK is such that the dynamic loader can work with both GTK2 and GTK3 depending on what's installed.
- Since we're accumulating a lot of library loaders I've built a generic interface as FModule which replaces TOptWin32Proc and the loaders in the OpenAL and Fluidsynth code.
The only reason this even existed was that ZDoom's original VC projects used __fastcall. The CMake generated project do not, they stick to __cdecl.
Since no performance gain can be seen by using __fastcall the best course of action is to just remove all traces of it from the source and forget that it ever existed.
