[Biopython] Dropping Python 2.3 support in Biopython

[Peter Cock]

Hello all,

This is a final warning that the next release of Biopython will not
support Python 2.3.

As far as we are aware, no-one has come forward with a need for
continued support for Python 2.3, so we will soon begin removing the
special case code needed to keep Biopython working on Python 2.3.
This will give us a simpler code base, less platforms to test on, and
we can also take advantage of various language features only available
in Python 2.4+ (e.g. generator expressions and decorators).

Any last minute requests to postpone this should be made to the main
Biopython mailing list by Friday 8 May.

Thank you,

Peter