[PATCH 0 of 3] RFC: forest extension (take 2)

[Robin Farine]

This series of patches proposes an updated version of the forest
extension for review and possibly for inclusion in Mercurial.

The first patch modifies Mercurial's util.walkrepos() so the extension
can use it rather than define its own version. This version of the
patch supersedes the version already posted to the list.

The second patch changes the same code to follow symbolic links while
looking for repositories. The extension does not depend on it but
users wanted to be able to populate trees with symbolic links to
repositories.

The third patch contains the extension itself, test case and test
results.