Remove unused code
Simplify hash code
Further simplify hash code
Rewrite hashing to use FT_Stream directly

This is more robust but introduces a small change in behavior:
For .pcf.gz fonts, the new code calculates the hash of the uncompressed
font data whereas the original code was calculating the hash of the
compressed data.

No big deal IMO.
Allow passing NULL for file to FcFreeTypeQueryFace()