'svn merge' error reporting

Simple bugs, and enhancements to error reporting.

Elsewhere error reporting

* Commit to an out-of-date DAV mirror:

svn: Commit failed (details follow):
svn: The specified baseline is not the latest baseline, so it may not be checked out.

* err && ! err->apr_err

Generated by mod_dav_svn:

svn: E000000: A reported revision is higher than the current repository HEAD revision.  Perhaps the repository is out of date with respect to the master repository?