Oops, the vertexdecoder should read vertex alpha.

Copy/paste mistake... ugh.
Don't forget tex alpha if only a mip has none.

Mip levels should only move toward unknown.
Avoid the GE debugger affecting vertexFullAlpha.
Use an unsigned compare for x86 vertexalpha check.
Merge pull request #6017 from unknownbrackets/texalpha

Fix a bunch of texture/vertex alpha issues