Exclude arguments from sfunc and finalfunc aggregate attributes. Fixes #54.

 * pyrseas/dbobject/function.py (Aggregate.create): Don't look for
   open paren in finalfunc.  (ProcDict.query): Use cast to regproc
   instead of regprocedure for aggtransfn and aggfinalfn.
 * tests/dbobject/test_function.py: Change tests to exclude arguments
   from sfunc and finalfunc attributes.