Support for Subversion 1.7.1

If using a working copy checked out with Subversion 1.7.1, comparing against SVN base is currently broken.

Qutoed from http://tortoisesvn.net/tsvn_1.7_releasenotes.html
"working copy metadata storage improvements
Subversion 1.7 features a complete re-write of the working copy metadata management system of Subversion, code named WC-NG.

Centralized Metadata Storage

A key feature of the changes introduced in Subversion 1.7 is the centralization of working copy metadata storage into a single location. Instead of a .svn directory in every directory in the working copy, Subversion 1.7 working copies have just one .svn directory—in the root of the working copy. This directory includes (among other things) an SQLite-backed database which contains all of the metadata Subversion needs for that working copy.

Even though the data is stored in a structured format, the relationships between the data are complex. We highly discourage external tools from modifying the data held in this database, as such modification is likely to result in working copy corruption."