The SCAN_FRAGREQ signal could possibly become very large when it
contains lots of index bounds in the keyInfo part. There is a hard
limit on ~32K for signals sent in a single chunk. In order to
overcome this limitation for huge SCAN_FRAGREQ, it could be sent
as a fragmented signal.

This patch change the SPJ block to use sendFragmentedSignal()
for sending SCAN_FRAGREQ. As the SPJ block may also send 
the same SCAN_FRAGREQ to multiple LQHs, it does not want the
sent signal data to be released after send (which is the normal behaviour).

Thus, sendFragmentedSignal() has been extended to take a 'noRelease'
argument to support the reuse of the send signal data. Note: most
of the underlying framework to support this was already implemented
in SimulatedBlock.

As a set of ranges defined for an index scan might now become
> 64K, we also had to change the struct RangeBuilder member m_range_size
from an Uint16 -> Uint32.