Import rbenv changes at 7e0e85bdda092d94aef0374af720682c6ea8999d
Revert a fix for #101 to fix broken tests relating to `PYENV_NATIVE_EXT`
Add pip-rehash
Update Makefile. Use same path configuration as travis-ci.
Merge pull request #280 from yyuu/rbenv-7e0e85bd

Import recent changes from rbenv