Move of TransactionContext concept to Geronimo

[David Jencks]

After discussion with Jeremy, I've moved the TransactionContext concept 
from Nova to Geronimo and started implementing the simplifications in 
Geronimo that this will make possible.  It appears to run fine for me 
on both Geronimo and Nova, but I do not rule out problems, especially 
with the recent SF problems of all descriptions.

Please let me know if this causes problems.
thanks
david jencks