title: Check for a subversion update
body: <p>I am putting together a build system and wanted to know if there is a reliable way to find out if a checked out SVN folder needs updating (i.e. is it out of sync with the repository).  I want to avoid a nightly build unless something has changed.  I could write a script that parses the results of the <code>svn update</code> command I guess, but I wondered if there as a command that would tell me if an update is actually required?</p>