bump up version to 1.3pre

 * minVersion to 17.0
 * maxVersion to 21.0a1
nsISupportsArray is removed from nsITreeView since Firefox 22. Closes #98

Firefox21-とFirefox22+の両対応として、`aProperties` がないなら、
`nsISupportsArray`を生成し、最後に文字列化して返す。
Merge branch 'devel/issue98' into develop
Merge branch 'develop'
release 1.2.1

 * maxVersion to 22.0a1