test-rebase-interruptions: stabilize for Windows
External hooks end up launching cmd.exe, which knows nothing about $VAR syntax.
For some reason, I thought that Mercurial would substitute in the value, in
order to paper over the platform difference. But I can't find that in the
documentation, and there's at least one other use of this pattern [1].
[1] https://www.mercurial-scm.org/repo/hg/file/tip/tests/test-histedit-fold.t#l477
$ hg init repo
$ cd repo
$ touch foo
$ hg ci -Am 'add foo'
adding foo
$ hg up -C null
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
this should be stored as a delta against rev 0
$ echo foo bar baz > foo
$ hg ci -Am 'add foo again'
adding foo
created new head
$ hg debugindex foo
rev offset length ..... linkrev nodeid p1 p2 (re)
0 0 0 ..... 0 b80de5d13875 000000000000 000000000000 (re)
1 0 13 ..... 1 0376abec49b8 000000000000 000000000000 (re)
$ cd ..