[Mpi-21] Small clarification in I/O chapter for external32

[Rajeev Thakur]

Alexander Supalov pointed out to me that the following sentence in the MPI-2
I/O chapter, under external32 data representation, pg 250 lines 24-25 is
misleading:

"All data items are stored contiguously in the file."

It is intended to mean that there is no prescribed alignment in the
resulting file (to word boundary, etc.). But the data is stored contiguously
only as long as the file view is contiguous. Accordingly, we propose to
clarify the sentence as follows, with the additional text in parenthesis:

"All data items are stored contiguously in the file (if the file view is
contiguous)."

Regards,
Rajeev