missing mkdirRecursive

[jkryl]

Normally mkdir is fast operation which can be executed synchronously without blocking event loop for too long time, but this holds only for "local filesystems". When trying to use wrench on a disk exported through iSCSI the delays can get noticeably longer and one needs to switch to async methods. I have a simple fix implementing mkdirRecursive function (only this function because that's the only function I'm using in my app from wrench). I will submit a pull request shortly.