CRM-12370 - add extension modules immediately after civicrm drupal module.

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* CRM-12370: CRM_Utils_Hook::requireCiviModules() assigns infinite weight to extensions
  https://issues.civicrm.org/jira/browse/CRM-12370
Merge pull request #3730 from wellebee/CRM-12370

CRM-12370 - add extension modules immediately after civicrm drupal modul...