Added tests to highlight Windows makeDirectory bug

The third test added here fails on Windows.  makeTree fails when an absolute path is given, as "mkdir C:\\" fails with EPERM, not EEXIST.  makeTree's implementation assumes that existing directories will fail with either EEXIST or EISDIR.  I'm not sure where best to fix it (in makeDirectory or makeTree).

This issue is currently blocking usage of minit on Windows as well (behind another bug, which I'll log shortly).

All tests pass on OSX.