deprecation warnings about trace.info and pb in merge

[Vincent Ladeuil]

Using bzr-loom with bzr.dev now emits deprecation warnings:
bzr up-thread
/home/vila/src/bzr/trunk/bzrlib/merge.py:241: UserWarning: pb parameter to Merger() is deprecated and ignored
  warnings.warn("pb parameter to Merger() is deprecated and ignored")
All changes applied successfully.
Moved to thread 'cleanup'.
/home/vila/.bazaar/plugins/loom/tree.py:134: DeprecationWarning: bzrlib.trace.info was deprecated in version 2.1.0.
  bzrlib.trace.info("This thread is now empty, you may wish to "
This thread is now empty, you may wish to run "bzr combine-thread" to remove it.

I have a fix and will do a merge proposal asap.

[Vincent Ladeuil (vila)]

See https://code.edge.launchpad.net/~vila/bzr-loom/528472-depreation-warnings/+merge/20222