EMI: clamp specialty textures

The specialty textures which are used in the intro need to be clamped
to avoid dark lines between the tiles.
EMI: Check another bit in the mesh face flags to enable blending.

Bit 0x40000 in the mesh face flags (set only in the intro) should
enable blending, too. This fix lets the various screens of the intro
fade into each other.
Merge pull request #1023 from chkr-private/intro-fixes

Intro fixes