Address a potential race in File.mkdirs() with a double exists() check

A complete solution will make mkdirs() atomic with some coordination,
which, currently, is counter to the desired architecture.
Merge pull request #9 from mattf/address-mkdirs-race

Address a potential race in File.mkdirs() with a double exists() check
Fixed recursive foreverness. Added Test Case
Revert "Fixed recursive foreverness. Added Test Case"

This reverts commit ffdd0de9633a77f35dba6eb0ed2ee844fc84dc3e.