- scanning for required include files is now down by directory rather

- scanning for required include files is now down by directory rather
  than by file, using -e to check for the existence for a file rather than
  doing an eq against every filename in the directory.
- previously we only checked a candidate include directory for freetype.h
  to consider it a valid FT1.x include directory.  We now check if it
  contains fterrors.h too, if it does, then it's from a FT2 installation
  and we ignore it.