VisualStudio .NET compile.
Added support for OSG_NOTIFY_LEVEL and OSG_FILE_PATH into the relevant getenv
routines. This compliments the exisiting OSGNOTIFYLEVEL & OSGFILEPATH which
are deprecated but still supported. The OSG_ version are more consistent
with the rest of the env variables used in the OSG.
routines - we now have FileUtils_Windows.cpp, FileUtils_Mac.cpp and
FileUtils_Unix.cpp. The FileUtils_Mac.cpp is based on code submitted
by Josh Portway and add uses the carbon API for searching for files.