Restored FFI to working order (#28)

* Restored FFI to working order

* Disabled incompatible tests, fixed string conversion

* Use extension_loaded instead of checking PHP version

* Added better checks for FFI

* Do not build FFI deps if no FFI is present

tests/common.inc

@@ -29,4 +29,10 @@ abstract class CrtTestCase extends PHPUnit_Framework_TestCase {
             $this->setExpectedException($arguments[0]);
         }
     }
+
+    public function skipFFI() {
+        if (CRT::isFFI()) {
+            $this->markTestSkipped();
+        }
+    }
 }