revlog: add a new test file focussed on testing transactionally issue
What we test here is currently also covered by `test-hooks.t`. However having
our own test file allow for more focussed/deep testing and to cover more variant
when relevant. So we create a new test file.
Differential Revision: https://phab.mercurial-scm.org/D10626
Test issue2761
$ hg init
$ touch to-be-deleted
$ hg add
adding to-be-deleted
$ hg ci -m first
$ echo a > to-be-deleted
$ hg ci -m second
$ rm to-be-deleted
$ hg diff -r 0
Same issue, different code path
$ hg up -C
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ touch does-not-exist-in-1
$ hg add
adding does-not-exist-in-1
$ hg ci -m third
$ rm does-not-exist-in-1
$ hg diff -r 1