Make typestate properly descend pattern guards

Closes #1265

Author: marijnh

src/comp/middle/tstate/pre_post_conditions.rs

@@ -452,6 +452,10 @@ fn find_pre_post_expr(fcx: fn_ctxt, e: @expr) {
       expr_alt(ex, alts) {
         find_pre_post_expr(fcx, ex);
         fn do_an_alt(fcx: fn_ctxt, an_alt: arm) -> pre_and_post {
+            alt an_alt.guard {
+              some(e) { find_pre_post_expr(fcx, e); }
+              _ {}
+            }
             find_pre_post_block(fcx, an_alt.body);
             ret block_pp(fcx.ccx, an_alt.body);
         }

src/comp/middle/tstate/states.rs

@@ -530,6 +530,12 @@ fn find_pre_post_state_expr(fcx: fn_ctxt, pres: prestate, e: @expr) -> bool {
         if vec::len(alts) > 0u {
             a_post = false_postcond(num_constrs);
             for an_alt: arm in alts {
+                alt an_alt.guard {
+                  some(e) {
+                    changed |= find_pre_post_state_expr(fcx, e_post, e);
+                  }
+                  _ {}
+                }
                 changed |=
                     find_pre_post_state_block(fcx, e_post, an_alt.body);
                 intersect(a_post, block_poststate(fcx.ccx, an_alt.body));