Fix one-item folders elimination in VS2010.
Fix one-item folders elimination in VS2010.

Introduced in fa94082, the elimination algorithm was broken: it would
still generated NestedProjects entry for eliminated folders. Fixed now.
Also fixed for the situation when a folder in the middle of a chain of
>2 subfolders is eliminated.

vslavik/bakefile,vslavik/bakefile,vslavik/bakefile