Increased precision of decimal fields
Added traps to Decimal quantization operations
Validating that a quantized Decimal value did not loose all non zero digits
Fixed failing tests in Python 2.6
Updated test cases to use custom JSONDecoder class
Fixed more Python 2.6 and Decimal problems
Kill DebitAccountMiddleware.
Merge branch 'develop' into feature/issue-818-kill-DebitAccountMiddleware

Conflicts:
	go/vumitools/middleware.py
Kill CreditManager.
Merge branch 'develop' into feature/issue-818-kill-DebitAccountMiddleware
Nuke obsolete context processor.
Allowing Twisted to handle any JSON encoding/decoding exceptions
Updated comment
Added calculate_credit_cost class method to MessageCost model
Added QUANTIZATION_EXPONENT setting
Moved credit_amount calculation from SQL to Python
Using MessageCost.calculate_credit_cost instead of repeating calculation
Merged with develop
Merge branch 'feature/issue-818-kill-DebitAccountMiddleware' into develop
Merge pull request #777 from praekelt/feature/issue-777-decimal-message-cost

Cannot add a decimal when defining messaging costs