Thank you + Minor update (foo, .xcent, fix "$2: unbound variable")

Heya,

Thank you for adding support for entitlements, I was just about to do it when I saw you have made a pull request on the original repo with exactly this :)

1. During the building process the .xcent file is generated from the Entitlements files, so if you re-sign, you would want to provide it as an .xcent (which in most cases would be identical to your entitlements file). So I just edited the "help line" to use the "foo" placeholder as the other argument for ".mobileprovision" does as well as rename the extension to ".xcent"

2. When I was using it for inspection only ("./ipa_sign -i File.ipa") I got error "$2: unbound variable" (Mavericks terminal), so I moved PROVISION="$(realpath "$2")" into the if statement and it solved it.

Cheers,
Doron