Bug 890795 - Actually disable the test where intended. r=logicfail
Bug 908920 - Don't assume suspended generator activations have a script. r=jorendorff

This patch makes legacy (JS 1.7) and star (ES6) generators have
different classes, avoiding the need to poke through to the frame's
script to see which kind they are.  This steps around a failure to get
a frame's script after GC, when the script was thrown away, while also
preparing for bug 907744.

To detect errors in the future, also make accesses to gen->fp->script()
cause a null pointer deref in debug mode.  This caught another bug in
generator_close_impl(), in which with GGC it could be possible to
reference a return value from the recently dead frame.  This was easily
fixed because that value is always undefined.
Bug 909452 - geolocation_common.js needs rewrite to pushPrefEnv. r=jmaher