Add support for specifying a ";" delimited list of scenery locations to

Add support for specifying a ";" delimited list of scenery locations to
search when loading scenery tiles.  (I am not set on using ";" as the
delimiter because it is a command separator in unix, but ":" is a critical
part of the windows file naming scheme (c:\foo\bar) so that is even worse.)

Example:

--fg-scenery=/stage/fgfs04/curt/Scenery-0.9.1/Scenery;/stage/helio1/curt/Scenery
-0.7.9