Ev2 shims: Make sure we use the proper base revision (if one is provided) when fetching base content for repos diff.
Ev2 shims: Make sure we use the proper base revision (if one is provided) when
fetching base content for repos diff.

Current number of Ev2 test failures: 1 (and it only happens on OS X)

* subversion/libsvn_client/repos_diff.c
  (fetch_kind_func, fetch_props_func, fetch_base_func): Use the base revision,
    if it is valid.

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion