Remove uses of .str(), .c_str() and some other methods of SGPath.
Pass SGPath directly where possible, or explicitly convert to the
appropriate 8-bit encoding.
Copies HELVETICA_12 from PLIB to FG, adding some more chars needed for
Latin1/ISO-8859-1 (West European languages).
(SANS_12B and HELVETICA_14 also support Latin1, but not the other default
PLIB fonts).