0030550: Coding - Integer overflow in Standard_CString HashCodes

0030550: Coding - Integer overflow in Standard_CString HashCodes
0030551: Foundation Classes - Integer overflow in NCollection_CellFilter HashCode

Signed integers are not used in hash code functions now to prevent undefined behavior on left shift operations with signed integers.
A possibility of negative values of hash codes is eliminated.
INT_MAX → IntegerLast() in hash code functions.
All found hash code functions behaves uniformly now: they return a value in the range [1, theUpperBound]. Relevant comments are added to such functions.