pgsql: Add traceback information to PL/Python errors

Add traceback information to PL/Python errors

This mimics the traceback information the Python interpreter prints
with exceptions.

Jan Urbański

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/2bd78eb8d51cc9ee03ba0287b23ff4c266dcd9b9

Modified Files
--------------
src/pl/plpython/expected/plpython_do.out           |    5 +-
src/pl/plpython/expected/plpython_error.out        |  193 +++++++++++++++-
src/pl/plpython/expected/plpython_error_0.out      |  193 +++++++++++++++-
.../plpython/expected/plpython_subtransaction.out  |   55 ++++-
.../expected/plpython_subtransaction_0.out         |   30 ++-
.../expected/plpython_subtransaction_5.out         |   30 ++-
src/pl/plpython/expected/plpython_test.out         |    5 +-
src/pl/plpython/expected/plpython_types.out        |    5 +-
src/pl/plpython/expected/plpython_types_3.out      |    5 +-
src/pl/plpython/plpython.c                         |  236 +++++++++++++++++---
src/pl/plpython/sql/plpython_error.sql             |  105 +++++++++
11 files changed, 786 insertions(+), 76 deletions(-)