Fix NewLocalRef, NewGlobalRef to handle cleared weak globals.

We were not checking for null after decoding the reference, this
meant that we incorrectly created null weak global references instead
of returning null.

Issue: 63929
Change-Id: I9159682e6edad8f415ef8144fc13b9aedd2cceb4
Remove old fork-and-specialize API

As promised, this is the cleanup patch-set which removes the
old native "fork and specialize" API, which has been replaced
by a slightly-enhanced one which can close the Zygote socket
descriptors in the Zygote child.

Change-Id: I096f058e851aa079e342ecc718ff5757db68c8cd
Merge "Fix NewLocalRef, NewGlobalRef to handle cleared weak globals." into cm-11.0
Merge branch 'cm-11.0' of https://github.com/CyanogenMod/android_art into cm-11.0
Merge branch 'cm-11.0' of https://github.com/temasek/android_art into cm-11.0