python - be: Cleanups and Fixes.

Log Message:
-----------
Cleanups and Fixes.

Fix a VPC-SRF bug where on every call the context callback would be registered.
This triggered to a strange exception in GC collection. (grr)

Don't attach the PL call to the fn_extra unless the return is an iterator; if
state need not be kept, don't keep it. (This could probably be revisited to
avoid the extra dictionary hit when the flinfo is merely being reused.)

Additionally, don't leak plc in pl.c, the call object. This may have been
masking other bugs.

Modified Files:
--------------
    be/include/pypg/type:
        system.h (r1.1 -> r1.2)
        (http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/python/be/include/pypg/type/system.h.diff?r1=1.1&r2=1.2)
    be/src:
        call.c (r1.7 -> r1.8)
        (http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/python/be/src/call.c.diff?r1=1.7&r2=1.8)
        heaptuple.c (r1.9 -> r1.10)
        (http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/python/be/src/heaptuple.c.diff?r1=1.9&r2=1.10)
        pl.c (r1.28 -> r1.29)
        (http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/python/be/src/pl.c.diff?r1=1.28&r2=1.29)
        tupledesc.c (r1.10 -> r1.11)
        (http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/python/be/src/tupledesc.c.diff?r1=1.10&r2=1.11)
    be/src/call:
        function.c (r1.8 -> r1.9)
        (http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/python/be/src/call/function.c.diff?r1=1.8&r2=1.9)
        pl.c (r1.14 -> r1.15)
        (http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/python/be/src/call/pl.c.diff?r1=1.14&r2=1.15)