Fix parsing of interpolated paths

src/test/run-pass/macro-path.rs

@@ -0,0 +1,16 @@
+mod m {
+    pub type t = int;
+}
+
+fn macros() {
+    macro_rules! foo {
+        ($p:path) => {
+            fn f() -> $p { 10 }
+            f()
+        }
+    }
+}
+
+fn main() {
+    assert foo!(m::t) == 10;
+}