[Rd] Mksetup() limited to hashing with 32 bits

[Benjamin Tyner]

The MKsetup() in unique.c throws an error if the vector to be hashed is 
longer than (2^32)/8:

    if(n < 0 || n > 536870912) /* protect against overflow to -ve */
        error(_("length %d is too large for hashing"), n);

I occasionally work with vectors longer than this on 64-bit builds. Would it be too much to ask that R can take advantage of all 64 bits for hashing when compiled as such?

Thanks
Ben