Merge branch 'new-solver' of gitlab.inria.fr:mavanzin/pwhile into new-solver

examples/pldi/bridge.imp

+# variation of random walk
+
+def bridge():
+  var a, b, n
+
+  while a < x and x < b:
+    tick 1
+    prob(1,1):
+      x = x - 1 
+    else:
+      x = x + 1
+