configure: Add a check for the DGifOpen function in the gif_lib.h header as the v4 of the file does define it, while v3 doesn't.

When using reserved areas the memory could potentially be reused right
after the release.

Implement D3DSIO_TEXREG2AR, TEXREG2GB, TEXREG2RGB, TEXM3X3TEX, TEXM3X3SPEC.

injected mouse move events. Fix a problem detected by the test.

- Use WINPOS_WindowFromPoint instead of WindowFromPoint in order to
  use hittest directly to simplify the code. 
- WM_NCMOUSEHOVER and WM_MOUSEHOVER take different parameters.