Corrected edef_io for Python 2.6 / ElementTree 1.2
Corrected edef_io for Python 2.6 / ElementTree 1.2

ElementTree 1.2.x misses some features used in EDEFWriter.
Those features are added when the module is loaded.
Also, the ElementTree module used in edef_io is removed from sys.modules
before it is modified, so that it doesn't modifies the behavior of the module
for the whole application.

ahmadshahwan/ipopo,tcalmant/ipopo,ahmadshahwan/ipopo