According to I/O API, QIODevice and its inherited classes should be
able to process a full 64-bit offsets and lengths. This requires
64-bit parameters in operations with internal buffers. Rework
QRingBuffer to avoid implicit truncation of numbers and fix some
64-bit issues in code.
Change-Id: Iadd6fd5fefd2d64e6c084e2feebb4dc2d6df66de
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>