Renamed fgParseOptions(int,string) to fgParseArgs, and modified the

Renamed fgParseOptions(int,string) to fgParseArgs, and modified the
function to allow property files as non-option parameters after the
options have finished (and added "--" to terminate options).  It's now
possible to do something like

  fgfs denver-am.fgd

or even

  fgfs at-lax.fgd in-c310.fgd around-sunset.fgd

This works the same way as the --config option, but will be friendlier
for GUIs, where start-up situation files can now be associated easily
with FlightGear.