[PATCH 0 of 2] Build on latesttag for archival and mercurial builds

[Gilles Moris]

As the implementation of the new version string required to somewhat undo the
previous patch, it did no more make sense to have incremental patches.

So even though this series now contains only 2 patches, patch 2 should still
be simple enough to review.

Matt,

Are you OK with the new version string scheme as a subset of:
tag+tagdist-hash+date
as described in patch 2 ?

Regards.
Gilles.