Iterate over folders in the PATH var.
Iterate over folders in the PATH var.

This also adds a test for msys-2.0.dll to be sure,
it's the expected folder.

Fixes #23

oneclick/rubyinstaller2,larskanis/rubyinstaller2,larskanis/rubyinstaller2,oneclick/rubyinstaller2,larskanis/rubyinstaller2,oneclick/rubyinstaller2