Enum::CONST(): never return same instance

Enums shouldn't be compared with ===, but static accessors are now
cached so === was working. Let's return a clone each time so === won't
be true for values retrieved from these accessors.

Note: this actually had no impact on the performance gains from a few
commits ago.

Author: danielbeardsley

src/Enum.php

@@ -232,7 +232,7 @@ public static function __callStatic($name, $arguments)
             }
             return self::$instances[$class][$name] = new static($array[$name]);
         }
-        return self::$instances[$class][$name];
+        return clone self::$instances[$class][$name];
     }
 
     /**

tests/EnumTest.php

@@ -143,6 +143,7 @@ public function testStaticAccess()
         $this->assertEquals(new EnumFixture(EnumFixture::FOO), EnumFixture::FOO());
         $this->assertEquals(new EnumFixture(EnumFixture::BAR), EnumFixture::BAR());
         $this->assertEquals(new EnumFixture(EnumFixture::NUMBER), EnumFixture::NUMBER());
+        $this->assertNotSame(EnumFixture::NUMBER(), EnumFixture::NUMBER());
     }
 
     /**