bfopen: save individual series' original metadata (rebased onto dev_4_4)



This is the same as gh-573 but rebased onto dev_4_4.

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Previously the union of all series' original metadata was stored once
for each series.  This causes potentially substantially more memory to
be used, and makes it more difficult to read original metadata.

See: http://lists.openmicroscopy.org.uk/pipermail/ome-users/2013-June/003816.html

/cc @sbesson