oops, remove a little bit test code
Include 'colspan' in the list of attributes
take out unncessary ImageComponet updates from the buildTexture methods
add some documentation in the build texture methods.  Make some expressions
in these methods a little more readable.
check missingTransparent (default=true) to determine color space dimension.  Transparent
missing values needs RGBA or Gray+Alpha (if we get it working).  Patch to
make this work for RGBComposite.  GraphicsModeControl and Display.MissingTransparent
are checked (the latter has precedence).
applyTexture: if constant_alpha=NaN (pick up transparency from table) then
setTransparency(0), the default in the attribute.