tests/test-diff-issue2761.t

lazymanifest: use a binary search to do an insertion

This makes insertions log(n) plus some memmove() overhead, rather than
doing an append followed by an n*log(n) sort. There's probably a lot
of performance to be gained by adding a batch-add method, which could
be smarter about the memmove()s performed.

Includes a couple of extra tests that should help prevent bugs.

Thanks to Martin for some significant pre-mail cleanup of this change.

Test issue2761

  $ hg init

  $ touch to-be-deleted
  $ hg add
  adding to-be-deleted
  $ hg ci -m first
  $ echo a > to-be-deleted
  $ hg ci -m second
  $ rm to-be-deleted
  $ hg diff -r 0

Same issue, different code path

  $ hg up -C
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ touch does-not-exist-in-1
  $ hg add
  adding does-not-exist-in-1
  $ hg ci -m third
  $ rm does-not-exist-in-1
  $ hg diff -r 1