Add test case for #2869 (xfailed)

Author: catamorphism

src/test/run-pass/issue-2869.rs

@@ -0,0 +1,14 @@
+// xfail-test
+enum pat { pat_ident(option<uint>) }
+
+fn f(pat: pat) -> bool { true }
+
+fn num_bindings(pat: pat) -> uint {
+    alt pat {
+      pat_ident(_) if f(pat) { 0 }
+      pat_ident(none) { 1 }
+      pat_ident(some(sub)) { sub }
+    }
+}
+
+fn main() {}