Correctly mask dead MDT chambers

The new conditions algorithms/object introduced a split between "dead chamber" (chamber with a dead element) and "dead station" (chamber entirely off) which was not present in the old muon conditions services. The MuonStationIntersectSvc wants to know if it should consider a chamber dead, but was calling a function ("isGoodChamber") that returns false if a multilayer/tube is off, but not if the entire chamber is off; the correct function to call (reproducing the conditions service behavior) is "isGoodStation". I have changed this.

In general the "isGoodChamber" function seems very dangerous - users will almost certainly expect it to do something other than what it does - but I didn't change it on the grounds that the interface design isn't my domain.