tests/test-issue842.t

merge: use operation-provided labels (ex: dest/source) in several merge-tools

Tools that did not use labels already, used only one, or used some label other
than the exact strings of "local" or "other" were unmodified.  Cases that used
the label "base" were modified as well, if they were otherwise changed in this
CL; "merged" was *not* changed.

There are other possible changes we might want to make, but I didn't:
- bcompare (linux and osx) uses the labels "parent1" and "parent2" instead of
  "local" and "other", so it was left alone, even though beyondcompare3
  (windows) *was* changed.
- araxis used the labels "Other", "Base", and "Local :$local", so it was also
  left alone.
- UltraCompare didn't provide a label for 'local', just for 'base' and 'other',
  so it was left alone.

Differential Revision: https://phab.mercurial-scm.org/D2012

https://bz.mercurial-scm.org/842

  $ hg init
  $ echo foo > a
  $ hg ci -Ama
  adding a

  $ hg up -r0000
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved

  $ echo bar > a

Should issue new head warning:

  $ hg ci -Amb
  adding a
  created new head

  $ hg up -r0000
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved

  $ echo stuffy > a

Should not issue new head warning:

  $ hg ci -q -Amc

  $ hg up -r0000
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved

  $ echo crap > a
  $ hg branch testing
  marked working directory as branch testing
  (branches are permanent and global, did you want a bookmark?)

Should not issue warning:

  $ hg ci -q -Amd