windows: Improve readability of the checkout-banshee script
windows: Improve readability of the checkout-banshee script

As the git command is itself a batch file on Windows, you need to use
"call" to call it from another batch file.

stsundermann/banshee,Dynalon/banshee-osx,dufoli/banshee,GNOME/banshee,Carbenium/banshee,GNOME/banshee,GNOME/banshee,stsundermann/banshee,babycaseny/banshee,ixfalia/banshee,babycaseny/banshee,arfbtwn/banshee,dufoli/banshee,Carbenium/banshee,mono-soc-2011/banshee,dufoli/banshee,arfbtwn/banshee,stsundermann/banshee,arfbtwn/banshee,dufoli/banshee,babycaseny/banshee,mono-soc-2011/banshee,Dynalon/banshee-osx,Dynalon/banshee-osx,Carbenium/banshee,stsundermann/banshee,arfbtwn/banshee,ixfalia/banshee,ixfalia/banshee,mono-soc-2011/banshee,arfbtwn/banshee,Dynalon/banshee-osx,dufoli/banshee,ixfalia/banshee,ixfalia/banshee,Carbenium/banshee,GNOME/banshee,babycaseny/banshee,stsundermann/banshee,dufoli/banshee,mono-soc-2011/banshee,GNOME/banshee,babycaseny/banshee,mono-soc-2011/banshee,babycaseny/banshee,GNOME/banshee,babycaseny/banshee,stsundermann/banshee,ixfalia/banshee,Carbenium/banshee,arfbtwn/banshee,mono-soc-2011/banshee,dufoli/banshee,stsundermann/banshee,Dynalon/banshee-osx,Dynalon/banshee-osx,mono-soc-2011/banshee,arfbtwn/banshee,ixfalia/banshee,babycaseny/banshee,stsundermann/banshee,arfbtwn/banshee,dufoli/banshee,Carbenium/banshee,Dynalon/banshee-osx,ixfalia/banshee,GNOME/banshee,Dynalon/banshee-osx,GNOME/banshee