Alter contribute.repeattransaction api to take amount and campaign_id as a parameter

The contribute.repeattransaction api is a relatively new addition to assist people in creating new instances of recurring transactions without every payment processor having to invent a method of copying line items etc.

Currently however, people can update the amount of the recurring transaction via the UI and, in the case of tokenised processors like eWay & IATS this causes the amount to change. However, copying the original transaction (currently in the BaseIPN method) gets the amounts & line items from the original rather than the changed amount.

We have discussed an improved mechanism for this - which involves storing line items against the recurring_contribution rather than the contribution (line item accepts entity_table other than contribution).

This is part of the spec Veda is working on.

http://wiki.civicrm.org/confluence/display/CRM/Offline+Recurring+Payments%3A+Implementation+Plan?focusedCommentId=249200671#comment-249200671

However, that is a 4.7 spec. This ticket proposes supporting the minimal situation where the total_amount is passed in AND there is only one line item - adjusting the stored amount. If there is more than one line_item current behaviour (to ignore the total amount) will be unchanged for now as part of keeping the scope of this change small

(note that in discussion the people affected by this were not currently dealing with situations where changes happened on single line items so it might be that situation doesn't really 'hit' before we are in a position to tell people to upgrade to 4.7