update font file checking to accept
1. optional offset (hence changes to getfontnum).
2. ignore lines truncated by end-of-buffer.
3. split and unsplit subfonts (faccess).

chkfont program included for careful font checking. chkfont
will report on which subfonts are invalid and do basic checking
of the subfont file but don't validate individula characters or
subfont character heights yet.