tcp: moved the "not enough space in rcv buffer" detection to a new function --- TRANSLATE!!!

identical change, for change detection easily
the current detection incorrect, doesn't check the overlap with existing slices
tcp: modified "not enough space in rcv buffer" detection

the old version didn't calculate with overlapped segments
tcpwestwood: changes based on tcpvegas fixes

- initialize and delete vectors
- added "existing of vector" checks
- create vector if not created
- signed/unsigned comparison
- removed unused local variables