Tried on nightly build of 1.7.4.
Add Kernel#__dir__. Fixes #651.
This isn't working with ruby --2.0 from a 1.7.5 install using RVM. I'm installing 1.7.6 now to see if it's fixed. 1.7.5 was returning nil.
Same for 1.7.6 installed through rvm
Definitely not working. Reopening to fix and add regression test.
Actually implement __dir__ using stack trace logic. Fixes #651