Fix existing privacy/visibility violations

This commit fixes all of the fallout of the previous commit which is an attempt
to refine privacy. There were a few unfortunate leaks which now must be plugged,
and the most horrible one is the current `shouldnt_be_public` module now inside
`std::rt`. I think that this either needs a slight reorganization of the
runtime, or otherwise it needs to just wait for the external users of these
modules to get replaced with their `rt` implementations.

Other fixes involve making things pub which should be pub, and otherwise
updating error messages that now reference privacy instead of referencing an
"unresolved name" (yay!).

src/librustdoc/html/render.rs

@@ -126,7 +126,7 @@ enum Implementor {
 /// to be a fairly large and expensive structure to clone. Instead this adheres
 /// to both `Send` and `Freeze` so it may be stored in a `RWArc` instance and
 /// shared among the various rendering tasks.
-struct Cache {
+pub struct Cache {
     /// Mapping of typaram ids to the name of the type parameter. This is used
     /// when pretty-printing a type (so pretty printing doesn't have to
     /// painfully maintain a context like this)