Record revisions of documents in macro definitions and usages. Then,
when searching for usages, check the revision of the documents against
the revision of the macros. If they are out-of-sync, repreprocess the
documents to get up-to-date info.

Task-number: QTCREATORBUG-7872
Change-Id: I846bb52ec660024728ab117a9fb7e43382a50e63
Reviewed-by: Christian Stenger <christian.stenger@digia.com>