python - be: Only pfree when recoding occurs.

Log Message:
-----------
Only pfree when recoding occurs.

This caused a double pfree when the server's encoding is ASCII. ASCII being a
compatible subset of utf-8, no transformation is necessary, so the function
simply returned the source.

Modified Files:
--------------
be/src:
pl.c (r1.46 -> r1.47)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/python/be/src/pl.c.diff?r1=1.46&r2=1.47)