#7 Allow class object as return from get_data_callback

[jason owens]

get_data_callback currently restricts return values to
arrayrefs of hashrefs/arrayrefs. This is limiting if
you are using a persistence framework /
object-relational mapping system. By simply changing
the code from ref() to UNIVERSAL::isa(), you can
preserve the semantics but allow classes in place of
strict hashrefs.

The patch modifies one line where this change is needed.

[jason owens]