Organize smt tests in subdirectories

test/libsolidity/smtCheckerTests/loops/while_loop_simple_4.sol

@@ -0,0 +1,11 @@
+pragma experimental SMTChecker;
+// Check that negation of condition is not assumed after the body anymore
+contract C {
+    function f(uint x) public pure {
+        while (x == 2) {
+        }
+        assert(x != 2);
+    }
+}
+// ----
+// Warning: (199-213): Assertion violation happens here\nNote that some information is erased after the execution of loops.\nYou can re-introduce information using require().