This is a draft for preliminary review.

…into mpio_develop

This is in response to one of the PR review comments.

…5Dmpio.c

(with the frees of the arrays moved to before the IO)
2) Move H5FD_selection_build_types() to H5FDmpio.c
This is in response to one of the PR review comments.

…into mpio_develop

…into mpio_develop

…into mpio_develop

….c when selection I/O is ON by default in the library.

a) Create internal functions H5FD_read/write_vector_from_selection() and H5FD_read/write_from_selection() that correspond to the 4 new APIs H5FDread/write_vector_from_selection() and H5FDread/write_from_selection().
--Call the internal functions H5FD_read/write_vector_from_selection in H5FD__mpio_read/write_selection() for independent xfer_mode.

…into mpio_develop

when selection I/O is ON by default in the library.
--Undo the base address addition in internal routines before passing down to the mpio driver

…/t_dsets.c (via testpar/testphdf5.c)

when selection I/O is ON by default in the library:
--need to check for fixed bufs when trying to figure out mpi_bufs_base in H5FD__selection_build_types().

…into mpio_develop

This is the fix for a failure from test_link_chunk_io_sort_chunk_issue() test in
testpar/t_coll_md.c (via testpar/testphdf5.c) when selection I/O is ON by default
in the library:
--need to check for fixed bufs when trying to figure out mpi_bufs_base in H5FD__selection_build_types().

…into mpio_develop

…ordingly.

system() is only used in the iopipe test and the things it calls
(which are POSIX-y) are protected by an ifdef.