support params in sql panel that cannot be JSON encoded by default JSONEncoder

[zt-initech]

If sql params are values that cannot be encoded by the built-in json.JSONEncoder, then the sql panel doesn't get the params and subsequently can't perform the query or EXPLAIN the query.

In my case, I often have params that are instance of datetime.datetime.

I currently use the following patch: zt-initech@47e7664

It is not very nice. I don't like using both JSON and pickle, and there are probably other problems.

How do you think this problem should be fixed?
For example, should params always be pickled?
Can you help me fix this patch to get it merged upstream?

[zt-initech]

This issue is probably related: #747