CRM-14355 fix test-exposed bugs in contribute, participant, pledge get

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* CRM-14355: make api treat limit = 0 as an unlimited request
  http://issues.civicrm.org/jira/browse/CRM-14355
Merge pull request #2702 from eileenmcnaughton/CRM-14355

CRM-14355 fix test-exposed bugs in contribute, participant, pledge get