fully-qualified font names for clients' benefit. Clients only pay for
    the font names once they request the FC_FILE property from an
    FcPattern, but the font name is malloc'd at that point (i.e. not
    mmapped: that's impossible, since it may vary between machines.)
    Clients do have to pay for a copy of the path name per cache file.
Note that FcPatternGetString now does some rewriting if you ask for an
    FC_FILE, appending the pathname as appropriate.