A new infrastructure for warnings.

On the user side, coqtop and coqc take a list of warning names or categories
after -w. No prefix means activate the warning, a "-" prefix means deactivate
it, and "+" means turn the warning into an error. Special categories include
"all", and "default" which contains the warnings enabled by default.

We also provide a vernacular Set Warnings which takes the same flags as argument.

Note that coqc now prints warnings.

The name and category of a warning are printed with the warning itself.

On the developer side, Feedback.msg_warning is still accessible, but the
recommended way to print a warning is in two steps:

1) create it by:

let warn_my_warning =
  CWarnings.create ~name:"my-warning" ~category:"my-category"
    (fun args -> Pp.strbrk ...)

2) print it by:

warn_my_warning args

1 files changed, 2 insertions, 1 deletions

diff --git a/kernel/cbytegen.ml b/kernel/cbytegen.ml
index a0ef5e570..8cbc3ab44 100644
--- a/kernel/cbytegen.ml
+++ b/kernel/cbytegen.ml
@@ -907,7 +907,8 @@ let compile fail_on_error ?universes:(universes=0) env c =
       Feedback.msg_debug (dump_bytecodes init_code !fun_code fv)) ;
     Some (init_code,!fun_code, Array.of_list fv)
   with TooLargeInductive tname ->
-    let fn = if fail_on_error then Errors.errorlabstrm "compile" else Feedback.msg_warning ?loc:None in
+    let fn = if fail_on_error then Errors.errorlabstrm "compile" else
+	       (fun x -> Feedback.msg_warning x) in
       (Pp.(fn
 	   (str "Cannot compile code for virtual machine as it uses inductive " ++
 	    Id.print tname ++ str str_max_constructors));