Mac: Partial rewrite of dw_exect(). Implement DW_EXEC_CON with Terminal.app. Previously we had been using xterm, which hasn't been included MacOS since 10.7 (Lion). Also, rewrite the DW_EXEC_GUI to allow more than one file to open.

[Desktop Entry]
Name=Dynamic Windows Test
Exec=@prefix@/bin/dwtest 
Terminal=false
MultipleArgs=false
Type=Application
Categories=Application;Development;X-Red-Hat-Base;