Prevent changing originalfile.mimetype from 'Directory'

[mtbc]

One should not be able to change a mimetype in the originalfile table from 'Directory' to some other value. Other changes should still be permitted.

See discussion on a92d503.

[bpindelski]

omero=# SELECT COUNT(*) FROM originalfile WHERE mimetype = 'Directory';
 count 
-------
     4
(1 row)

omero=# UPDATE originalfile SET mimetype = 'foobar' WHERE mimetype = 'Directory';
ERROR:  Directory(20)=/root_0/ must remain a Directory

Looks ok to merge.

[joshmoore]

@mtbc: thoughts on bumping the patch version, etc? What other changes are upcoming from your side?

[mtbc]

Other changes depend on what we do about some of the beta2 tickets, really. (Import set, for instance.) I thought about bumping the patch version, but it won't break things or not to have the trigger there, so I figured it probably wasn't worth it, it just causes me to have a reason to break out a 5.0DEV6 → ? upgrade script separately from my 4.4 -> 5.0DEV6 one. I could still bump it if you like though.

[joshmoore]

Fair enough and makes good sense. It's almost guaranteed that there will be some other DB change, so we'll integrate this change then. In the mean-time, however, no one will be testing this in anger, so the only possibly thing to look out for is a decrease in delete performance. /cc @pwalczysko

[mtbc]

--no-rebase as it changes DB