This is a subversion core api since 1.4, to run it with 1.2 and 1.3 we have a copy
here that is doing the same with ra do_diff instead of do_diff2.

client.h file            copied/based from subversion 1.2.0 subversion\libsvn_client
repos_diff_summarize.cpp copied       from subversion 1.4.0 subversion\libsvn_client

It is copied here because client.h is not a public subversion header and we don't
want a dependency on a header that is not installed with a subversion binary
distribution.

The complete folder can be removed when Subcommander requires subversion 1.4 as
minimum api.
