The current version of the Subversion software (svn) on our servers was 1.4.2 which at the time of writing is the version found in the RHEL 5 rpm repository (rhel-x86_64-server-5).

This is old, old, old and does not include lots of goodies that the latest version of svn contains...

http://subversion.apache.org -  
"Subversion 1.5 is a superset of all previous Subversion releases, and is considered the current "best" release. Any feature or bugfix in 1.0.x through 1.4.x is also in 1.5, but 1.5 contains features and bugfixes not present in any earlier release."

(I was later to find that the 1.5 version had also been superceded but at this point I was blissfully ignorant of this fact. The point is I wanted to upgrade.)

The first thing to realise is that the latest version of svn lives in a different repository called rpmforge which is accessed after installing the rpmforge-release package. 

Unfortunately the package I installed from http://rpmrepo.org/RPMforge/Using was not the most recent version.

wget http://packages.sw.be/rpmforge-release/rpmforge-release-0.5.1-1.el5.rf.x86_64.rpm rpm -Uhv http://packages.sw.be/rpmforge-release/rpmforge-release-0.5.1-1.el5.rf.x86_64.rpm

I found this out when I realised that subversion was missing from the rpmforge repository and I what I actually wanted was in a sub repository called rpmforge-extras which was not accessible using the version of rpmforge package I had installed (rpmforge-release-0.5.1-1)

Thanks be to  http://www.mail-archive.com/users@lists.rpmforge.net/msg01908.html!

Basically you have to update rpmforge by using

yum --enablerepo=rpmforge update rpmforge-release

This now makes rpmforge-extras available so you can now do the install after telling it to ignore the old version found in the RHEL5 repository

yum --enablerepo=rpmforge-extras --disablerepo=rhel-x86_64-server-5 install subversion mod_dav_svn

I had some conflicts with the previous version. I probably could have done an update but I chose to clean up by listing the installed subversion packages with

yum list subversion

and then getting rid of them with 

yum remove subversion.i386
yum remove subversion.x86_64

Now I was able to install the latest version of subversion and its apache module - we're now on svn 1.6. 

The other main gotcha was the url used to access the repository. I went through loads of port checking on the firewall before I realised our old version of svn was so old that the apache module didn't work and so we'd used the svnserve sofware server solution on a dedicated port. All our scripts were using svn://... Once changed to http://... it worked like a dream, or am I dreaming?