Remove duplicate PMF exception logic and make use of DN "singleton PMF" handler

DataNucleus has a handler to allocate singleton PMFs. If you set a persistence property "datanucleus.singletonPMFForName" then it will hand out a singleton instance of that PMF. If you subsequently try to create a PMF with that name then it returns the current (active) PMF for that name.

This patch removes the previous exception logic and makes use of the builtin singleton handler. The tests are updated to test allocation of a singleton, and allocation of a non-singleton.

[maxr, 2011-07-12 10:52:48]

On 2011/07/12 07:35:17, datanucleus wrote:

Nice, I take it there's no similar property for JPA?

Also, for some reason the side-by-side diffs aren't working for your patch.  I
downloaded your patch, applied it, and when I ran upload.py the side-by-side
diffs are there:
http://codereview.appspot.com/4699044/

Are you uploading code the same way?

[datanucleus, 2011-07-12 11:05:11]

There is an equivalent property for JPA, but just not done that one yet ;-)

I upload the patch via the "Data" button on the form, and not via any Python
script. If I look at the text of the patch file it is correctly formed, so no
idea what the form does with it