Fix crash with ETQW and Quake 4
make it compile with clang; fix a memory leak cppcheck foud
Avoid the case c0 == c1 when encoding

This case may break buggy decoders.
Fix for #2 (alpha zero pixels wreaking havoc).

One place accidentally ignored alpha-zero pixels, making it inconsistent
with the rest and causing bad visual errors in MODE_FAST.
Fix a weird bug in selecting initial colors by wrong order of loads/stores.
reenable alpha 0 pixel ignorance for DXT1

As DXT1 never stores color values where alpha is 0.
Fix some warnings, fixes #3
Merge branch 'master' into s2tc+alpha

Conflicts:
	s2tc_algorithm.cpp