22-jun-2006 NvE Linear track storage facility introduced in AliSignal to enable

22-jun-2006 NvE Linear track storage facility introduced in AliSignal to enable
                a lightweight signal <-> track backward linking facility instead of
                the elaborate signal slot related links.
                Also the functionality of AliTrack::AddSignal extended with specific modes.
                Double_t replaced by Double32_t in Ali3Vector.h, Ali4Vector.h and AliBoost.h
                and fDresult suppressed for I/O streaming. This will reduce the produced
                output filesize.
22-jun-2006 NvE Bi-directional links for signals <-> tracks set via the new lightweight
                AliSignal::AddTrack facility instead of AddLink in IceF2k.
                Also default split level set to 0 in IceF2k to minimise file size and
                I/O time.
23-jun-2006 NvE New lightweight AliSignal::AddTrack facility used in IceLinefit and IceDwalk.