wip: Attempting to prevent C extensions from loading on Rbx.
More updates to address the Rubinius/C-extensions bug.
Rbx seems to be broken on Travis again.
Fixed buggy extension guard.
Better warnings when loading C extensions.
Fixed broken require.
Merge pull request #153 from ruby-concurrency/native-extension-aliases

Fix bug #150 -- Erroneous C extension behavior on Rubinius.