Testcase for Silicon issue 883 (#821)

Author: mlimbeck

src/test/resources/all/issues/silicon/0883.vpr

@@ -0,0 +1,16 @@
+field f: Int
+
+@moreJoins("2")
+method foo(x: Ref, xs: Set[Ref])
+    requires forall r: Ref :: { r in xs } r in xs ==> acc(r.f)
+{
+    var b: Bool
+    inhale acc(x.f, 1/2)
+    if (b) {
+        inhale acc(x.f, 1/2)
+    } else {
+        inhale acc(x.f, 1/2)
+    }
+
+    assert acc(x.f)
+}