CRM-12370 - Reapply 2991458

See also: #552, #560, #570

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* CRM-12370: CRM_Utils_Hook::requireCiviModules() assigns infinite weight to extensions
  http://issues.civicrm.org/jira/browse/CRM-12370
CRM-12370 - Code style

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* CRM-12370: CRM_Utils_Hook::requireCiviModules() assigns infinite weight to extensions
  http://issues.civicrm.org/jira/browse/CRM-12370
Merge pull request #572 from totten/hook-errors-redux

CRM-12370 - Fix another regression from new hook code