Temporarly restore '-undefined dynamic_lookup' when building libXrdProofd.so. Linking in libXrd.a
  is not correct for XrdProtocol plug-ins (and also does not work).
  Some issues ned to be solved on the xroot side before we can remove '-undefined dynamic_lookup'.


git-svn-id: http://root.cern.ch/svn/root/trunk@40331 27541ba8-7e3a-0410-8455-c3a389f83636