[SMTChecker] Refactor CHC loops and add if blocks

test/libsolidity/smtCheckerTests/loops/while_nested_continue.sol

@@ -0,0 +1,28 @@
+pragma experimental SMTChecker;
+
+contract C
+{
+	function f(uint x, uint y, bool b, bool c) public pure {
+		require(x < 10);
+		while (x < 10) {
+			if (b) {
+				x = 20;
+				continue;
+			}
+			else {
+				require(y < 10);
+				while (y < 10) {
+					if (c) {
+						y = 20;
+						continue;
+					}
+					y = 15;
+					break;
+				}
+				assert(y >= 15);
+				x = y;
+			}
+		}
+		assert(x >= 15);
+	}
+}