Make score computation at the python level

[codersquid]

euroscipy/symposion has a couple of changes, and I'm opening issues for them. I don't know if this change fixes a problem (the other one did).
euroscipy@112123b

[brosner]

@codersquid thank you for the report! Can you provide more details about why we need to ditch ProposalScoreExpression in favor of the Python version?

[codersquid]

@brosner Hi, I haven't actually looked in to the commit from @pdebuyl. I opened this issue since they had fixed something in one of the other commits, and I don't want to any of their other fixes to get lost. This change may just be a preference versus a fix. I've been hoping for some time to dig in to it.

[pdebuyl]

This part of the code was broken for EuroSciPy 2014. I didn't explain the bug in the commit message which is a bit annoying in retrospect.

From memory, I can think of two causes:

• The Decimal module complained with an error.
• The sql request refused to execute.

As I couldn't fix those problems, I saw the Python way as simpler and more robust.