tests/test-issue1089.t

filemerge: raise InMemoryMergeConflictsError if we hit merge conflicts in IMM

Merge conflicts might be supported in the future, but for now are kept out of
scope.

Any places where we used to call `flushall()` should be replaced with some kind
of exception. At this point, IMM M1 is no longer supported.

Differential Revision: https://phab.mercurial-scm.org/D1212

https://bz.mercurial-scm.org/1089

  $ hg init
  $ mkdir a
  $ echo a > a/b
  $ hg ci -Am m
  adding a/b

  $ hg rm a
  removing a/b (glob)
  $ hg ci -m m a

  $ mkdir a b
  $ echo a > a/b
  $ hg ci -Am m
  adding a/b

  $ hg rm a
  removing a/b (glob)
  $ cd b

Relative delete:

  $ hg ci -m m ../a

  $ cd ..