++expecta/specta to arm64 branches

Conflicts:
	external/expecta
Remove test that boxes _Bool into NSValue
Removed traces of RACExtensions since they're part of the core framework now.
Merge pull request #978 from ReactiveCocoa/fix-bool-lifting

Fix _Bool lifting test
Merge pull request #982 from ReactiveCocoa/remove-traces-of-racextensions

Removed traces of RACExtensions since they're part of the core framework now.
Merge pull request #989 from corristo/flatten-last-sync-signal-bug

Fix and failing test case for #988
Failing testcase for #988