OPENGL: Properly use signed types for cursor hotspot.
OPENGL: Use signed types for mouse coordinates.

This adjusts for the fact that our event handling also uses signed coordinates.
OPENGL: Use GLfloat for draw cooridnates in Texture.
OPENGL: Simplify shake offset application.
OPENGL: Use frac_t for cursor scaling.
OPENGL: Move RGBA8888 (logical layout) to OpenGL specific formats.

The reason here is that GL_UNSIGNED_INT_8_8_8_8 is not supported by the GLES
standard. Thus we cannot use it outside OpenGL specific code paths.
OPENGL: Always support RGBA8888 (memory layout).
OPENGL/SDL: Default to RGBA8888 (memory layout).

This makes sure the default mode also works for OpenGL ES contexts.
WINTERMUTE: Use game format for fallback font rendering.

BDF fonts got 32bit drawing support in ece8b7fb65402238ab7df896361a9cefe28b8897
Thus it is not necessary to draw onto a 16bit surface.
AVALANCHE: Rename/implement rest of getMe().
AVALANCHE: Silence GCC warnings

Mainly, GCC complained about case labels having a value less than
the minimum value for the type. Probably because character literals
may be signed or unsigned, while _trigger is always unsigned.
AVALANCHE: Made comments ASCII friendly

The comments I introduced earlier (previusly case labels) have been
changed to avoid non-ASCII characters. The descriptions were taken
from an ISO 8859-1 manual page.
AVALANCHE: Implement keyboard control in Help.
FULLPIPE: More work on scene09_initScene()
FULLPIPE: Even more work on scene09_initScene()
FULLPIPE: Implement scene09_setupGrit()
FULLPIPE: Further work on scene09_initScene()
FULLPIPE: Plug scene09 in
FULLPIPE: Implement scene09_updateCursor()
FULLPIPE: Implement sceneHandler09_updateScreenCallback()