Fix clamping to the correct texel.

This fixes things when edges bleed in from a larger framebuffer.  We need
to clamp to the internal texels of the range.
When projecting textures, flip V in frag shader.

Slower, but this way we actually project correctly.
Merge pull request #6254 from unknownbrackets/framebuf-clamp

Correct framebuf clamping, tex projection from framebuf