python - be: Move the XD(transaction dict) feature to the PL.

Log Message:
-----------
Move the XD(transaction dict) feature to the PL.

Reasoning is that this is a convenience rather than a real interface, so it
seems appropriate to give it to the PL, rather than making it a part of the
interface extension.

Doing this allows the riddance of the XactHook inside the extension module.

Modified Files:
--------------
be/include/pypg:
externs.h (r1.6 -> r1.7)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/python/be/include/pypg/externs.h.diff?r1=1.6&r2=1.7)
be/src:
module.c (r1.10 -> r1.11)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/python/be/src/module.c.diff?r1=1.10&r2=1.11)
pl.c (r1.9 -> r1.10)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/python/be/src/pl.c.diff?r1=1.9&r2=1.10)