[RFC] Merge History Audit and Query

http://subversion.tigris.org/merge-tracking/func-spec.html#merge-history-audit

While Hyrum is looking at the "Commutative Author and Revision
Reporting" features, I'd decided to take a look at spec'ing out some
of the other auditing features. Specifically:

- Show change sets available from a merge source.

- Show where a change set has been merged to.

I'm considering the following command-line UI for these features:

svn info --merged-to [SOURCE@REV]
Show a list of merge targets (URL@REVs) that SOURCE has been merged to.

svn info --merged-from [TARGET@REV]
Show a list of merge sources (URLs) and corresponding revision range
lists that have been merged into TARGET.

Alternately, we could add a new 'svn audit' (or some such)
sub-command, instead of re-using 'svn info'. Thoughts?