tests/test-revlog-group-emptyiter.t

reachableroots: use internal "revstates" array to test if rev is a root

The main goal of this patch series is to reduce the use of PyXxx() function
that is likely to require ugly error handling and inc/decref. Plus, this is
faster than using PySet_Contains().

  revset #0: 0::tip
  0) 0.004168
  1) 0.003678  88%

This patch ignores out-of-range roots as they are in the pure implementation.
Because reachable sets are calculated from heads, and out-of-range heads raise
IndexError, we can just take out-of-range roots as unreachable. Otherwise,
the test of "hg log -Gr '. + wdir()'" would fail.

"heads" argument is changed to a list. Should we have to rename the C function
as its signature is changed?

Issue1678: IndexError when pushing

setting up base repo
  $ hg init a
  $ cd a
  $ touch a
  $ hg ci -Am a
  adding a
  $ cd ..

cloning base repo
  $ hg clone a b
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd b

setting up cset to push
  $ hg up null
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ touch a
different msg so we get a clog new entry
  $ hg ci -Am b
  adding a
  created new head

pushing
  $ hg push -f ../a
  pushing to ../a
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 0 changes to 0 files (+1 heads)

  $ cd ..