Declaremods: some more minor cleanup

 Some code cleaning and factorisation , comments, indentations, ...

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@16440 85f007b7-540e-0410-9357-904b9bb8a0f7
code simplifications concerning Summary

 - Most of the time, the table registered via Summary.declare_summary
   is just a single reference. A new function Summary.ref now allows
   to both declare this ref and register it to summary in one shot.

 - Clarifications concerning the role of [init_function].
   For statically registered tables that don't need a special initializer,
   just do nothing there (see the new Summary.nop function).

 Beware: now that Summary exports a function named "ref", any code that
 do an "open Summary" will probably fail to compile.

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@16441 85f007b7-540e-0410-9357-904b9bb8a0f7