Added a new VFD feature flag (H5FD_FEAT_SUPPORTS_SWMR_IO) that declares
SWMR-compatibiity. H5Fopen/create will now fail when H5F_ACC_SWMR_READ
or H5F_ACC_SWMR_WRITE are set as flags with H5Fcreate or H5Fopen and
the VFD does not support SWMR.

VFDs that are listed as supporting SWMR in this check-in:

    core, direct, log, sec2

Also includes a test for the flag's functionality in test/test_swmr.c.