hdf5_msb

(A) Fixes for the assertion failures described in issue #2 (see John Mainzer's last checkin message):
--src/H5PB.c: checks for size >= page size
--src/H5MF.c: disable/enable page buffering in H5MF_tidy_self_referential_fsm_hack()
--src/H5MFsection.c: call H5PB_remove_entry() for both raw/metadata pages in H5MF__sect_small_merge()
(B) Port and modify existing concurrent swmr tests to VFD SWMR. Also modify the following:
--remove flushes from VFD SWMR writer tests
--set Nreaders to 0 in test/testvfdswmr.sh.in to test for writers only
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