A tentative uniform naming policy in module Inductiveops.

- realargs: refers either to the indices of an inductive, or to the proper args
  of a constructor
- params: refers to parameters (which are common to inductive and constructors)
- allargs = params + realargs

- realdecls: refers to the defining context of indices or proper args
  of a constructor (it includes letins)
- paramdecls: refers to the defining context of params (it includes letins)
- alldecls = paramdecls + realdecls