Don't copy hidden files/directories during `setup.py install`
This is useful if a copy of Mercurial is stored in a Subversion repository
so that the .svn directories don't get copied.
adding a/b/c/d/x
adding a/b/c/d/y
adding a/b/c/d/z
moving a/b/c/d/x to z/b/c/d/x
moving a/b/c/d/y to z/b/c/d/y
moving a/b/c/d/z to z/b/c/d/z