Add failing test for broken KVO implementations.
Remove stack depth counter.
Simplify the feedback ignoring logic.
Revert "Add failing test for broken KVO implementations."

This reverts commit 737567fded0c76a2c2170cae8a1d992d0d847c68.
Added test for NSController support.
Merge pull request #895 from ReactiveCocoa/remove-stack-depth

Remove stack depth counter in RACKVOChannel