Test for #2723. Closes #2723

Author: catamorphism

src/test/auxiliary/issue_2723_a.rs

@@ -0,0 +1,3 @@
+unsafe fn f(xs: ~[int]) {
+  xs.map(|_x| { unsafe fn q() { fail; } });
+}

src/test/run-pass/issue-2723-b.rs

@@ -0,0 +1,8 @@
+// aux-build:issue_2723_a.rs
+
+use issue_2723_a;
+import issue_2723_a::*;
+
+fn main() unsafe {
+  f(~[2]);
+}