Add namespace ops.

Check if typecheck returned nothing for top-level form.
Improve error message.

svn: r10160

original commit: 1da9a0c4b84ea15e608a83028c07c75885082b29

collects/typed-scheme/private/base-env.ss

@@ -478,6 +478,9 @@
      
      [exit (-> (Un))]
      
+     [module->namespace (-> -Sexp -Namespace)]
+     [current-namespace (-Param -Namespace -Namespace)]
+     
      ;; syntax operations
      
      [expand (-> (-Syntax Univ) (-Syntax Univ))]

collects/typed-scheme/typed-scheme.ss

@@ -118,6 +118,7 @@
               (free-identifier=? #'head #'require)
               (free-identifier=? #'head #'provide)
               (free-identifier=? #'head #'begin)
+              (void? type)
               (type-equal? -Void (tc-result-t type)))
           body2]
          ;; construct code to print the type