revlog: finer computation of "issnapshot"
If the parent had an empty diff, we skip of it to compute a diff against the
parent base. This create shorter and simpler chain.
However these case could be wrongly detected as snapshot. So we improve the code
doing this detection.
In practice nobody care as when tried on a copy of mozilla-try and we got the
same number of snapshot (1315) in both case.
Performance where equivalent.
Issue1678: IndexError when pushing
setting up base repo
$ hg init a
$ cd a
$ touch a
$ hg ci -Am a
adding a
$ cd ..
cloning base repo
$ hg clone a b
updating to branch default
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ cd b
setting up cset to push
$ hg up null
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ touch a
different msg so we get a clog new entry
$ hg ci -Am b
adding a
created new head
pushing
$ hg push -f ../a
pushing to ../a
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 0 changes to 0 files (+1 heads)
$ cd ..