tests/test-manifest-merging.t

commit: try hard to reuse p1 manifest if nothing changed

This is all for commit reproducibility on "hg convert".

With this change, p1 manifest is reused if ctx.files() *to be committed* is
empty, and if new manifest entry is identical to p1. This is important
property for "hg convert" since memctx.files() built from a convert source
may be either a) more narrowed thanks to a committed ctx.files() which
provides more accurate status, or b) containing redundant files because of
sloppy filtering on e.g. octopus merge.

  $ hg init base

  $ cd base
  $ echo 'alpha' > alpha
  $ hg ci -A -m 'add alpha'
  adding alpha
  $ cd ..

  $ hg clone base work
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved

  $ cd work
  $ echo 'beta' > beta
  $ hg ci -A -m 'add beta'
  adding beta
  $ cd ..

  $ cd base
  $ echo 'gamma' > gamma
  $ hg ci -A -m 'add gamma'
  adding gamma
  $ cd ..

  $ cd work
  $ hg pull -q
  $ hg merge
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)

Update --clean to revision 1 to simulate a failed merge:

  $ rm alpha beta gamma
  $ hg update --clean 1
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved

  $ cd ..