Test for char array expressions containing if_expr in VCC

The added test are failing with versions of the string solver that
would not take into account if expressions.

Author: romainbrenguier

regression/strings-smoke-tests/java_if/test.class

@@ -0,0 +1,9 @@
+CORE
+test.class
+--refine-strings --string-max-length 100
+^EXIT=10$
+^SIGNAL=0$
+^\[.*assertion.1\].* line 12.* SUCCESS$
+^\[.*assertion.2\].* line 13.* FAILURE$
+--
+$ignoring\s*char\s*array

regression/strings-smoke-tests/java_if/test.desc

@@ -0,0 +1,16 @@
+public class test
+{
+    public static String main()
+    {
+        Object t[] = new Object[5];
+        t[0] = "world!";
+        StringBuilder s = new StringBuilder("Hello ");
+        if(t[0] instanceof String)
+        {
+            s.append((String) t[0]);
+        }
+        assert(s.toString().equals("Hello world!"));
+        assert(!s.toString().equals("Hello world!"));
+        return s.toString();
+    }
+}