Force jgit.sh to use UTF-8 encoding on Mac

For some obscure reason the platform encodng in Java on Macs
is MacRoman. OS X used UTF-8 as the default encoding so set
the encoding property in jgit.sh.

Change-Id: I08182c2f8512f799178cee70bcc28d6ee2b9c2b0

org.eclipse.jgit.pgm/jgit.sh

@@ -80,6 +80,7 @@ Darwin)
 			-Dcom.apple.mrj.application.growbox.intrudes=false
 			-Dapple.laf.useScreenMenuBar=true
 			-Xdock:name=JGit
+			-Dfile.encoding=UTF-8
 		'
 	fi
 	;;