Support nested cursor

[harawata]

By specifying "CURSOR" to jdbcType attribute.

<resultMap id="blogResult" type="Blog">
  <id property="id" column="id" />
  <result property="title" column="title" />
  <collection property="posts" column="posts" jdbcType="CURSOR">
    <id property="id" column="id" />
    <result property="subject" column="subject" />
    <result property="body" column="body" />
  </collection>
</resultMap>

<select id="selectBlog" resultMap="blogResult">
  select b.id, b.name, cursor(
    select p.id, p.subject, p.body from post p where p.blog_id = b.id
  ) posts from blog b
</select>

See the attached test cases for more examples.

Should fix #566

[coveralls]

coverage: 87.22% (-0.1%) from 87.326%
when pulling 03dc3e4 on harawata:gh/566-oracle-nested-cursor
into d4af490 on mybatis:master.