The python bindings do not currently support retrieval of the rpn expression in COMPU...

The python bindings do not currently support retrieval of the rpn expression in COMPUTE data sources. Attached is a patch that duplicates functionality from rrd_info.c to expose the correct data source attributes via the python binding. It:

    * exposes the rpn expression in the 'cdef' element for DST_CDEF data source types
    * exposes the heartbeat, min, and max only to the other data source types

git-svn-id: svn://svn.oetiker.ch/rrdtool/branches/1.2/program@1410 a5681a0c-68f1-0310-ab6d-d61299d08faa