CRM-15466 add test to ensure net_amount is set correctly
CRM-15446 fix for net_amount not being set
CRM-15446 additional test to check minor restructure of defaults
api example updates
CRM-15446 fix test to reflect actual returned value
remove unused parameter (no other calls to this fn)
fix membership_type to be editable within tests so we can address test failure
to get tests to pass add a hack-around to allow us to clear static var
minor tidy ups
Merge pull request #4351 from eileenmcnaughton/CRM-15446

CRM-15446 ensure net_amount always set on create contribution