moving fraction field to new coercion broke old pickles

[craigcitro]

At some point, fraction fields were moved over to the new coercion model, which is good -- except that it broke all the old pickles. This thread on sage-support is about someone having a problem with them:  http://groups.google.com/group/sage-support/browse_thread/thread/b5519db45a141819

The problem is that the old pickles don't have _element_class or _element_constructor fields, and there was no factory function in place -- so unpickling tries to directly create the object, which totally fails. Putting the old __call__ method back in place is an ugly hack to get these to load, but it's not a good permanent solution.

[mabshoff]

Hmm,

how did this escape the pickle jar doctest?

Cheers,

Michael