Ignore "CVS" directories within the repository.

CVS stores some kinds of metadata in "CVS" subdirectories within
repository directories (for example, whether a file is locked or
watched).  These directories are not part of the source tree and
contain no information useful to the conversion, so ignore them.

Patch by: David Morris <david@morrisonthenet.com>
Simplified by: me
Researched by: Olli Hauer <ohauer@gmx.de>

git-svn-id: http://cvs2svn.tigris.org/svn/cvs2svn/trunk@5434 be7e6eca-30d4-0310-a8e5-ac0d63af7087