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
$ hg init
$ echo This is file a1 > a
$ hg add a
$ hg commit -m "commit #0"
$ ls -A
.hg
a
$ echo This is file b1 > b
$ hg add b
$ hg commit -m "commit #1"
$ hg co 0
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
B should disappear
$ ls -A
.hg
a