Returning commit info from libsvn_client via a callback

["Hyrum K. Wright" <hy...@mail.utexas.edu>]

I've started looking at issue 1199, the ability to delete urls from
multiple repositories using one command line invocation.  This led me
to the following thought:

In the client API, any function which generates a commit returns a
single svn_commit_info_t as an output parameter.  One of the problems
for issue 1199 is that we don't have a way to notify of the several
commits which might be generated by such usage.  To correct this, I'm
contemplating adding a callback to return the commit info from
svn_client_delete3().  More generally, we may eventually have other
client APIs which generate multiple commits in a single invocation,
commit descending into externals, for instance.  This makes me want to
lean toward a standard solution.

As a result, I'd like propose a callback (possibly part of the client
context) which is used to handle commit info that gets returned.  This
would result in churn to a number of client APIs, but would allow for
their future extensibility, and consistency across the 1.7 (or future)
libsvn_client API set.  We've got other priorities now, but I'm
interested in the general reaction to this approach.

-Hyrum