[S] Upgrade Security to Python 2.6

[pjkersha]

Ref:  http://proj.badc.rl.ac.uk/badc/ticket/21574

There is at least one known issue with a 3rd party library:

• PyXML, is a dependency on ZSI. ZSI is itself used by NDG Security but NDG Security doesn't use PyXML directly. Instead it uses 4Suite-XML as a replacement XML parser. It may be possible to get ZSI to ignore it's PyXML dependency or else patch PyXML directly. The problem is a simple one to fix: the PyXML code contains an as local variable but from Python 2.6 onwards as is a reserved keyword.

[pjkersha]

2.x.x releases and the trunk run under Python 2.6