WINTERMUTE: Speeding up blitting routines for TransparentSurface
COMMON: Copy TransparentSurface from Wintermute engine to common code
WINTERMUTE: Switch to use of moved to OSystem TransparentSurface
SWORD25: Switch to common TransparentSurface
Merge pull request #466 from sev-/transparent-surface

COMMON: Move TransparentSurface to common code