Ensure that the declared type and actual type of a constant agree

Closes #899

Author: marijnh

src/comp/middle/typeck.rs

@@ -2479,6 +2479,9 @@ fn check_const(ccx: @crate_ctxt, _sp: span, e: @ast::expr, id: ast::node_id) {
           mutable fixups: fixups,
           ccx: ccx};
     check_expr(fcx, e);
+    let cty = expr_ty(fcx.ccx.tcx, e);
+    let declty = fcx.ccx.tcx.tcache.get(local_def(id)).ty;
+    demand::simple(fcx, e.span, declty, cty);
 }
 
 // A generic function for checking the pred in a check

src/test/compile-fail/bad-const-type.rs

@@ -0,0 +1,4 @@
+// error-pattern:expected str but found int
+
+const i: str = 10;
+fn main() { log i; }