[PATCH 0 of 5] Build on latesttag for archival and mercurial builds

[Gilles Moris]

Resend patch series availabale at:
http://thread.gmane.org/gmane.comp.version-control.mercurial.devel/25947
with the following modifications:

It includes feedback from Mads on coding style, mainly for patch 1 and 5.
Additionally, the support of local tags in hg_archival has been dropped, as
its utility was questionable.

The rest is mainly rewording of the commit messages.