i777: Allow installation on SGH-S959G

Don't let the 959 fool you - that's not a Vibrant!!!

Yes, that's right, Samsung used nearly identical model
numbers for two totally different devices.  T959 = Vibrant,
S959G = Straight Talk GS2.

It turns out the Straight Talk GS2 is nothing more than an
I777 with a sane bootloader (uses the recovery partition).

Flashing any I777-compatible kernel to the recovery partition
provides working recovery, and it has been confirmed that
I777 CM10.1 is fully functional on the S959G.

Change-Id: I790d23a2f3fe704bb1b5b4c75805f8d7c20b8740