hdf5_msb

Perform the dataset opens in reverse order to their creation, and if
H5Dopen fails, rapidly retry up to 9,999 times.  Log H5Dopen failures,
but log no more than once every five seconds to avoid spamming the
terminal.

With these changes, it's easier for the reader to open the last dataset
before the writer created it, but the reader recovers instead of
quitting with an error.  It should only be necessary to retry opening
the *last* dataset; all previous datasets should open on one try if the
last is open.