Import updated version of XROOTD, including some crucial fixes in the
client ReadV code.
To build do: make distclean-netx distclean-proofd distclean-proofx.


git-svn-id: http://root.cern.ch/svn/root/trunk@20315 27541ba8-7e3a-0410-8455-c3a389f83636