Added support for pending changesets

Created originally on Bitbucket by sdorra (Sebastian Sdorra)

Was already merged in Bitbucket before import, marked as merged by the import user

This patch sets the HG_PENDING environment variable at the start of the server. The HG_PENDING variable is needed to get changesets which are pending and not yet committed to the repository, e.g for pretxnchangegroup hooks.

Have a look at the following links:

• https://bitbucket.org/mirror/mercurial/src/9837cafc25b1/mercurial/localrepo.py?at=default#cl-322
• http://selenic.com/pipermail/mercurial/2010-June/033251.html