tests/test-merge4.t

import: wrap a transaction around the whole command

Now 'rollback' after 'import' is less surprising: it rolls back all of
the imported changesets, not just the last one. As an extra added
benefit, you don't need 'rollback -f' after 'import --bypass', which
was an undesired side effect of fixing issue2998 (59e8bc22506e)..

Note that this is a different take on issue963, which complained that
rollback after importing multiple patches returned the working dir
parent to the starting point, not to the second-last patch applied.
Since we now rollback the entire import, returning the working dir to
the starting point is entirely logical. So this change also undoes
a732eebf1958, the fix to issue963, and updates its tests accordingly.

Bottom line: rollback after import was weird before issue963,
understandable since the fix for issue963, and even better now.

  $ hg init
  $ echo This is file a1 > a
  $ hg add a
  $ hg commit -m "commit #0"
  $ echo This is file b1 > b
  $ hg add b
  $ hg commit -m "commit #1"
  $ hg update 0
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ echo This is file c1 > c
  $ hg add c
  $ hg commit -m "commit #2"
  created new head
  $ hg merge 1
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ rm b
  $ echo This is file c22 > c
  $ hg commit -m "commit #3"