Exclude DEFAULT arguments from function identifier in YAML output. Fixes #53.

 * pyrseas/dbobject/function.py (Function.create): Use allargs if
   present.  (ProcDict.query): Use pg_get_function_identity_arguments
   for arguments attribute and add pg_get_function_arguments as
   allargs.  (ProcDict._from_catalog): Exclude allargs if identical to
   arguments.
 * tests/dbobject/test_function.py: New test to verify mapping of
   DEFAULT arguments.
 * tests/dbobject/test_owner.py: New test to verify CREATE/ALTER of a
   function with DEFAULT arguments.