From Gerri:

This small patch allows to use a XROOTD version different from the one
shipped with ROOT to build the client (--with-xrootd=<alternative_dist>).
This is a first step to be more flexible with XROOTD ...


git-svn-id: http://root.cern.ch/svn/root/trunk@12863 27541ba8-7e3a-0410-8455-c3a389f83636