CRM-13090 uniqueness on title + activity type + campaign (optional). Moved the petition form rule to Petition form class where it belongs (was put in Survey/Results for some reason ??).

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* CRM-13090: New Petition/Survey form validation - enforce unique constraint on ActivityType-Campaign-Title
  http://issues.civicrm.org/jira/browse/CRM-13090
CRM-13090 add comment on public var.

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* CRM-13090: New Petition/Survey form validation - enforce unique constraint on ActivityType-Campaign-Title
  http://issues.civicrm.org/jira/browse/CRM-13090
Merge pull request #1305 from davecivicrm/CRM-13090

CRM-13090 uniqueness on title + activity type + campaign (optional).