romio gpfs: select correct read buffer

ROMIO GPFSMPIO_P2PCONTIG threaded read needs to toggle first read buffer

When using both the GPFSMPIO_P2PCONTIG and GPFSMPIO_PTHREADIO
optimizations there was a correctness bug when reading where for the
first round the read buffer did not toggle to the two-phase buffer for
the pthread reader, resulting in diseminating the data from the wrong
buffer.  The fix is to do the toggle after the first read.
Signed-off-by: Paul Coffman <pkcoff@us.ibm.com>
Signed-off-by: Rob Latham <robl@mcs.anl.gov>

src/mpi/romio/adio/common/p2p_aggregation.c

@@ -667,6 +667,7 @@ void ADIOI_P2PContigReadAggregation(ADIO_File fd,
 		ADIO_ReadContig(fd, read_buf,amountDataToReadThisRound,
 			MPI_BYTE, ADIO_EXPLICIT_OFFSET, currentRoundFDStart,
 			&status, error_code);
+        currentReadBuf = 1;
 
 #ifdef ROMIO_GPFS
 		endTimeBase = MPI_Wtime();