pgsql: Drop support for Python 2.3

Drop support for Python 2.3

There is no specific reason for this right now, but keeping support for
old Python versions around indefinitely increases the maintenance
burden. The oldest supported Python version is now Python 2.4, which is
still shipped in RHEL/CentOS 5 by default.

In configure, add a check for the required Python version and give a
friendly error message for an old version, instead of relying on an
obscure build error later on.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/04aad401867ad3e1519615d8486e32b50dbcb5f5

Modified Files
--------------
config/python.m4 | 1 +
configure | 4 ++++
configure.in | 3 +++
.../hstore_plpython/expected/hstore_plpython.out | 8 ++------
contrib/hstore_plpython/sql/hstore_plpython.sql | 8 ++------
doc/src/sgml/installation.sgml | 6 +-----
src/pl/plpython/expected/plpython_ereport.out | 24 +++++++++-------------
src/pl/plpython/plpy_typeio.c | 10 ++-------
src/pl/plpython/sql/plpython_ereport.sql | 8 ++------
9 files changed, 27 insertions(+), 45 deletions(-)