Now glob_sign and interp_sign only depend on structures defined
upto Genarg, so moved them there. This will allow defining the new
genarg interface.

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@16584 85f007b7-540e-0410-9357-904b9bb8a0f7
Implementing a new interface for Genarg, with centralized data
structure. The code is quite dumb for now, as it only handles basic
extended generig arguments (ExtraArgTypes). Soon, code from other
modules will be centralized there.

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@16585 85f007b7-540e-0410-9357-904b9bb8a0f7
Removing the various glob/subst/interp registering functions for
extra argument types and putting them into Genarg.

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@16586 85f007b7-540e-0410-9357-904b9bb8a0f7