configure: check for supported Python 2.x versions

The tracetool code requires Python 2.4, which was released in 2004.
Check for a supported Python version so we can give a clear error
message.

Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Reviewed-by: Lluís Vilanova <vilanova@ac.upc.edu>
