CRM-12108 minor improvement - simplify ipn.php by putting logic in the
relevant classes (no logic behind the split)
CRM-12108 noticed type on 'skipDefault' was wrong
CRM-12108 noticed api.contribution_recur.frequency_interval needs to be mandatory

Conflicts:

	api/v3/ContributionRecur.php
CRM-12108 noticed api.contribution_recur.start_date needs to be set or have a default - am defaulting to now