[PATCH 2 of 3 V2] merge: remove directory recursively, if there is no one other than directories

[Siddharth Agarwal]

On 05/15/2013 08:44 AM, FUJIWARA Katsunori wrote:
> # HG changeset patch
> # User FUJIWARA Katsunori <foozy at lares.dti.ne.jp>
> # Date 1368632246 -32400
> #      Thu May 16 00:37:26 2013 +0900
> # Node ID 185f02ec640199455dabfb80ebaca407f1249f82
> # Parent  06f5233fe026033740b5f7ee77234bd0a9b02016
> merge: remove directory recursively, if there is no one other than directories

I'm uncomfortable with file system modifications happening in 
_checkunknown, or really at all during the calculate phase. mpm needs to 
comment here.

Also maybe call the new function rmemptydirs or similar?