Remove 2GB limit from QByteArray

With the ubiquity of 64 bit compilers and abundance of memory in modern desktop systems, it would seem to be appropriate to remove the old 2GB limit on QByteArray sizes.  Perhaps embedded 32 bit environments could stay with 32 bit integer sizes for memory allocation, but in the desktop it seems a shame to have to abandon QByteArray when the contained data slips past the 2GB size boundary.