[build] Fix locale used for the generation of translators.xml
[build] Fix locale used for the generation of translators.xml

"en_US.utf8" is an invalid locale for FreeBSD, "en_US.UTF-8" is valid on
both Linux and FreeBSD (BGO#592587).

Signed-off-by: Bertrand Lorentz <eb7ac131ef7bff6d2ebccd6e5bf9a7cb6485cf2c@gmail.com>

GNOME/banshee,arfbtwn/banshee,GNOME/banshee,directhex/banshee-hacks,directhex/banshee-hacks,mono-soc-2011/banshee,mono-soc-2011/banshee,Carbenium/banshee,mono-soc-2011/banshee,arfbtwn/banshee,Dynalon/banshee-osx,stsundermann/banshee,petejohanson/banshee,GNOME/banshee,babycaseny/banshee,ixfalia/banshee,arfbtwn/banshee,stsundermann/banshee,Dynalon/banshee-osx,stsundermann/banshee,ixfalia/banshee,babycaseny/banshee,directhex/banshee-hacks,directhex/banshee-hacks,stsundermann/banshee,petejohanson/banshee,GNOME/banshee,Carbenium/banshee,arfbtwn/banshee,Dynalon/banshee-osx,babycaseny/banshee,babycaseny/banshee,allquixotic/banshee-gst-sharp-work,allquixotic/banshee-gst-sharp-work,dufoli/banshee,babycaseny/banshee,Carbenium/banshee,dufoli/banshee,dufoli/banshee,arfbtwn/banshee,directhex/banshee-hacks,petejohanson/banshee,mono-soc-2011/banshee,arfbtwn/banshee,GNOME/banshee,ixfalia/banshee,mono-soc-2011/banshee,ixfalia/banshee,ixfalia/banshee,GNOME/banshee,eeejay/banshee,ixfalia/banshee,lamalex/Banshee,ixfalia/banshee,Carbenium/banshee,eeejay/banshee,lamalex/Banshee,mono-soc-2011/banshee,GNOME/banshee,Dynalon/banshee-osx,allquixotic/banshee-gst-sharp-work,Carbenium/banshee,eeejay/banshee,stsundermann/banshee,petejohanson/banshee,stsundermann/banshee,dufoli/banshee,dufoli/banshee,lamalex/Banshee,eeejay/banshee,dufoli/banshee,lamalex/Banshee,petejohanson/banshee,eeejay/banshee,stsundermann/banshee,lamalex/Banshee,Dynalon/banshee-osx,Dynalon/banshee-osx,dufoli/banshee,Carbenium/banshee,GNOME/banshee,babycaseny/banshee,dufoli/banshee,stsundermann/banshee,babycaseny/banshee,allquixotic/banshee-gst-sharp-work,allquixotic/banshee-gst-sharp-work,mono-soc-2011/banshee,petejohanson/banshee,lamalex/Banshee,Dynalon/banshee-osx,Dynalon/banshee-osx,allquixotic/banshee-gst-sharp-work,babycaseny/banshee,ixfalia/banshee,arfbtwn/banshee,directhex/banshee-hacks,arfbtwn/banshee