Find system fonts (only works on Linux and Win32 at the moment)
Find fonts in paths, or the system paths if not given
XXX Doesn’t current support OS-X system paths
Get system font directories on Linux/Unix
Uses /usr/sbin/chkfontpath to get the list of system-font directories, note that many of these will not be truetype font directories.
If /usr/sbin/chkfontpath isn’t available, uses returns a set of common Linux/Unix paths