Removed not needed variable and work in standard library.
Found by Cppcheck (that variable's value was never used).
Replaced use of strcmp() with SDL_strcmp() in tests.
Removed not needed SDL_WINDOW_SHOWN from test programs.
See bug #1667.
Replaced use of malloc()/free() with SDL_malloc()/SDL_free() in test program.
Changed documentation comment for SDL_CreateShapedWindow().
See bug #1667.