Update gdk-pixbuf to 2.30.0
gtk+3 --without-atk-bridge no longer valid

the --without-atk-bridge parameter is no longer valid according to the
configure script output.
DarwinProfile: Default to 64bit on OS X

OS X has been 64 bit for quite a while, it is about time we joined the
future.
Mono: stack size in Mavericks is 512kb

The ugliest backport ever of:

https://github.com/mono/mono/commit/d6673ca8ec854f291eb32c048446b3868b92
de7a

https://github.com/mono/mono/commit/fe80190fc4d2f880c92f06ecc94aa33d1ecb
acb6
gmp: only force 32bit if building on 64bit machine targetting 32bit