Added Sys_FreeClipboardData(char*) so I don't have to copy the string
from SDL_GetClipboardText() into a Mem_Alloc() buffer, but can just
do the right thing per platform, which in case of POSIX/SDL2 is
SDL_free().
SDL1.2 doesn't have clipboard support, otherwise I'd have removed all
platform-specific implementations and used SDL_Get/SetClipboardText()
everywhere (IIRC AROS only supports SDL1.2?)
Don't include the lazy precompiled.h everywhere, only what's
required for the compilation unit.
platform.h needs to be included instead to provide all essential
defines and types.
All includes use the relative path to the neo or the game
specific root.
Move all idlib related includes from idlib/Lib.h to precompiled.h.
precompiled.h still exists for the MFC stuff in tools/.
Add some missing header guards.
