Add BuiltinBounds to closure type: parse and handle subtyping,

but do not integrate with kindck etc (requires a snapshot first)

src/test/compile-fail/closure-bounds-not-builtin.rs

@@ -0,0 +1,8 @@
+
+trait Foo {}
+
+fn take(f: &fn:Foo()) {
+    //~^ ERROR only the builtin traits can be used as closure or object bounds
+}
+
+fn main() {}

src/test/compile-fail/closure-bounds-subtype.rs

@@ -0,0 +1,34 @@
+fn take_any(_: &fn()) {
+}
+
+fn take_copyable(_: &fn:Copy()) {
+}
+
+fn take_copyable_owned(_: &fn:Copy+Owned()) {
+}
+
+fn give_any(f: &fn()) {
+    take_any(f);
+    take_copyable(f); //~ ERROR expected bounds `Copy` but found no bounds
+    take_copyable_owned(f); //~ ERROR expected bounds `Copy+Owned` but found no bounds
+}
+
+fn give_copyable(f: &fn:Copy()) {
+    take_any(f);
+    take_copyable(f);
+    take_copyable_owned(f); //~ ERROR expected bounds `Copy+Owned` but found bounds `Copy`
+}
+
+fn give_owned(f: &fn:Owned()) {
+    take_any(f);
+    take_copyable(f); //~ ERROR expected bounds `Copy` but found bounds `Owned`
+    take_copyable_owned(f); //~ ERROR expected bounds `Copy+Owned` but found bounds `Owned`
+}
+
+fn give_copyable_owned(f: &fn:Copy+Owned()) {
+    take_any(f);
+    take_copyable(f);
+    take_copyable_owned(f);
+}
+
+fn main() {}