[Truffle] Lots of ObjectSpace specs.
[Truffle] Update ignore file.
Merge branch 'master' of jruby.org:jruby
Revert "Revert "[Truffle] Abstract the safepoint mechanism so other features can re-use it.""

This reverts commit 3fb763ad42434f67f59edcc3585317ab9050d5a5.
[Truffle] Work on Thread specs.