[JENKINS-777] Add ability to set depth and ignore externals for a svn module.

This is based on the commit b2ac2f82a of the hudson subversion plugin.
Make UpdateUpdater make depth changes sticky.

Prior to this change the behaviour of changing the svn depth of a module
was inconsistent between UpdateUpdater and CheckoutUpdater.  Now they
both set the depth stickily.
Update svn book refs to latest version.
Merge pull request #29 from petdr/jenkins-777

[FIXED JENKINS-777] Add ability to set depth and ignore externals for a module