xrootd: revet back to 3.2.4

Signed-off-by: David Abdurachmanov <davidlt@cern.ch>
Merge pull request #123 from davidlt/IB/CMSSW_7_0_X/stable

[CMSSW_7_0_X] XROOTD revert back to 3.2.4
Merge remote-tracking branch 'origin/IB/CMSSW_7_0_X/stable' into IB/CMSSW_7_0_X/devel-gcc472