Bug fix to accept $ in 0th pos, (ie #ast{$(x) + ...}).

Note: part from Niko Matsakis commit: rewrite assert to accept a $ in
0th pos.

src/comp/syntax/ext/qquote.rs

@@ -184,11 +184,12 @@ fn finish<T: qq_helper>
     let sp = node.span();
     let qcx = gather_anti_quotes(sp.lo, node);
     let cx = qcx;
-    let prev = 0u;
-    for {lo: lo, _} in cx.gather {
-        assert lo > prev;
-        prev = lo;
+
+    // assert that the vector is sorted by position:
+    uint::range(1u, vec::len(cx.gather)) {|i|
+        assert cx.gather[i-1u].lo < cx.gather[i].lo;
     }
+
     let str2 = "";
     enum state {active, skip(uint), blank};
     let state = active;

src/test/run-pass/qquote.rs

@@ -81,6 +81,13 @@ fn main() {
     let x = #ast{1};
     let test1 = #ast{1+$(x)};
     check_pp(test1, pprust::print_expr, "1 + 1");
+
+    let test2 = #ast{$(x)+1};
+    check_pp(test2, pprust::print_expr, "1 + 1");
+
+    let y = #ast{2};
+    let test3 = #ast{$(x) + $(y)};
+    check_pp(test3, pprust::print_expr, "1 + 2");
 }
 
 fn check_pp<T>(expr: T, f: fn(pprust::ps, T), expect: str) {