pgsql: Modernize Python exception syntax in documentation

Modernize Python exception syntax in documentation

Change the exception syntax used in the documentation to use the more
current

    except Exception as ex:

rather than the old

    except Exception, ex:

We keep the old syntax in the test code since Python <2.6 is still
supported there, but the documentation might as well use the modern
syntax.

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/b55413d77f96b9fa2dfae4ddec43412b90ebf588

Modified Files
--------------
doc/src/sgml/plpython.sgml | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)