librustc: Enforce privacy for static methods.

This starts moving a bunch of privacy checks into the privacy
checking phase and out of resolve.

src/test/compile-fail/static-method-privacy.rs

@@ -0,0 +1,11 @@
+mod a {
+    pub struct S;
+    impl S {
+        static fn new() -> S { S }
+    }
+}
+
+fn main() {
+    let _ = a::S::new();    //~ ERROR function `new` is private
+}
+