The Mercurial fetcher previously used the revision number supplied by Mercurial
as its revision count. This is inappropriate, as the revision number is
incremented each time a change is added to the local repository, so also
changes only reachable from other heads will be counted. For the same reason,
it will also depend on whether such changes have been fetched before from the
same repository, introducing an impurity. Instead the revisions have to be
counted explicitly, similar to the Git fetcher.
Change-Id: Idb1e66ae2fb8b05101116c815f453efd6e95b09e
Alois Wohlschlager
54fac65fca