rebase: do not invent successor to skipped changeset

When rebase results in an empty a changeset it is "skipped" and no related
changeset is created at all. When we added obsolescence support to rebase (in
fc2a6114f0a0) it seemed a good idea to use its parent successor as the
successors for such dropped changesets. (see old version of the altered test).
This option was chosen because it seems a good way to hint about were the
dropped changeset "intended" to be. Such hint would have been used by automatic
evolution mechanism to rebase potential unstable children.

However, field testing of this version are not conclusive. It very often leads
to the creation of (totally unfounded) evolution divergence. This changeset
changes this behavior and mark skipped changesets as pruned (obsolete without
successors). This prevents the issue and seems semantically better probably a
win for obsolescence reading tool.

See example bellow for details:

User Babar has five changesets of interest:
- O, its current base of development.
- U, the new upstream
- A and C, some development changesets
- B another development changeset independent from A

    O - A - B - C
      \
        U

Babar decides that B is more critical than the A and C and rebase it first

  $ hg rebase --rev B --dest U

B is now obsolete (in lower case bellow). Rebase result, B', is its
successors.(note, C is unstable)

    O - A - b - C
      \
        U - B'

Babar is now done with B', and want to rebase the rest of its history:

  $ hg rebase --source A --dest B'


hg rebase process A, B and C. B is skipped as all its changes are already contained
in B'.

    O - U - B' - A' - C'

Babar have the expected result graph wise, obsolescence marker are as follow:

    B -> B' (from first rebase)
    A -> A' (from second rebase)
    C -> C' (from second rebase)
    B -> ?? (from second rebase)

Before this changeset, the last marker is `B -> A'`. This cause two issues:

- This is semantically wrong. B have nothing to do with A'
- B has now two successors sets: (B',) and (A',). We detect a divergent
  rewriting. The B' and A' are reported as "divergent" to Babar, confusion
  ensues. In addition such divergent situation (divergent changeset are children
  to each other) is tricky to solve.

With this changeset the last marker is `B -> ø`:

- This is semantically better.
- B has a single successors set (B',)

This scenario is added to the tests suite.
repoview: cache filtered changelog

Creating a new changelog object for each access is costly and prevents efficient
caching changelog side. This introduced a x5 performance regression in log
because chunk read from disk were never reused. We were jumping from about 100
disk read to about 20 000.

This changeset introduce a simple cache mechanism that help the last changelog
object created by a repoview. The changelog is reused until the changelog or the
filtering changes.

The cache invalidation is much more complicated than it should be. But MQ test
show a strange cache desync. I was unable to track down the source of this
desync in descent time so I'm not sure if the issue is in MQ or core. However
given the proximity to the 2.5 freeze, I'm choosing the inelegant but safe route
that makes the cache mechanism safer.
rebase: lose the comparison to `nullmerge`

For a proper behavior of the `--rev` revision we will need another possible
state for revision ignored by rebase. We alter the comparison to `nullmerge`
to match this future lower state too.
rebase: properly handle unrebased revision between rebased one

With rebase taking multiple roots it is possible to have revision in the "rebase
domain" not rebased themself. We do not want rebased revision above them to be
detached. We want such revision to be rebased on the nearest rebased ancestors.
This allows to preserve the topology of the rebase set as much a possible

To achieve this we introduce a new state `revignored` which informs
`defineparents` of the situation.

The test in `test-rebase-obsolete.t` was actually wrote and his now fixed.
run-tests.py: backout "don't use console for stdin when running in debug mode"

f5842787a958 caused that some kind of interactive debugging no longer was
possible - such as running hg with --debugger in a test run with run-tests.py
--debug .
run-tests.py: don't let hg run interactively in debug mode

In normal test mode stdin is closed and hg is thus not interactive. In --debug
mode stdin is inherited from the running console and to the tests, and hg could
thus wait in prompts when running on Windows.

See http://selenic.com/pipermail/mercurial-devel/2013-January/047548.html .

Instead set ui.interactive=False to make Mercurial non-interactive. Other
commands might still work differently in the --debug environment.

This should solve the problem with hg waiting for input but still make it
possible to add --debugger to hg in a test and run run-tests.py with --debug.
scmutil: localize and improve 'not under root' message