KEYID token makes parsing more robust in face of notations

A notation may introduce a new keyword that masks an quasi keyword
(IDENT "of" for example) used in some grammar rules.  KEYID "of"
acepts both "of" as an ident and "of" as a keyword.  Rephrasing grammar
rules with KEYID makes hence them more robust in face of user notations.

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/branches/v8.4@16588 85f007b7-540e-0410-9357-904b9bb8a0f7
parse "of" as KEYID "of"

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/branches/v8.4@16589 85f007b7-540e-0410-9357-904b9bb8a0f7