Modify THcDC, THcDriftChamber, THcSpacePoint

THcSpacePoint
  1) added fSetStubFlag which is intialized
     to kFALSE in constructor and set to kTRUE
     when SetStub is called.
   2) added method GetSetStubFlag which
      returns fSetStubFlag.

THcDriftchamber
   1) In ProcessHits increased fHits reserve to 40
   2) In FindSpacePoints use fSpacePoints->Delete();
   3) In LeftRight ,only SetStub if the Stub is fit.

THcDC
   1) In LinkStubs
      a) only link stubs if number of total spacepoints <10
      b) only link stubs if both spacepoints have SetStubFlag true

THcDCHit.h
   1) In constructor initalize fLR to 0

THcDCTrack.cxx
   1) AddSpacePoint check if fnSP < 10