CRM-13294 fix membership to support IN format on contact_id

Conflicts:

	tests/phpunit/api/v3/MembershipTest.php
test fix on api_v3_ContributionTest.testCompleteTransaction api_v3_ContributionTest.testCompleteTransaction
Merge pull request #1526 from eileenmcnaughton/master

CRM-13294 - extra fix + test fix