title: How to update Subversion externals
body: <p>We have several subversion repositories: one for common code and one for each top level project.  The top level projects have a svn:external link to the trunk of the common repository.</p>
  
  <p>Before we build a release of a project we create a branch of the top level project and also create a parallel branch in the common repository.</p>
  
  <p>How can we automatically ensure the svn:external property in the branched top level project points to the parallel branch in the common directory - currently it will be pointing to "trunk" in the common respository.  We are currently having to manually edit this in the branched project.</p>
  
  <p>Thanks</p>