Backwards-compatible enhancement to the asTrapWrite API to provide
listener routines with the data being put by the client.
The asTrapWriteMessage structure is extended with 3 new fields
for data type, element count and a pointer to the source buffer.
Tim Mooney requested this enhancement for his caPutRecorder code,
which doesn't work if the record overwrites the new value within
its process() routine, e.g. when jogging a motor record.
c5ded30684