SPARK-10262 Add @Since annotation to ml.attribute

[ghost]

@SInCE annotations for ml.attribute. Most appear to belong 1.4.0 with several exceptions. Please review.

https://issues.apache.org/jira/browse/SPARK-10262

[srowen]

(Please give this a more complete title and description, as in the JIRA)

[SparkQA]

Test build #1867 has finished for PR 9046 at commit eb37a0d.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds the following public classes (experimental):
  • sealed abstract class AttributeType(@Since("1.4.0") val name: String)

[mengxr]

@hucares This could be my fault. Do you see any non-DeveloperApi under ml.attribute?

[ghost]

@mengxr There are only DeveloperApi and now Since annotations under ml.attribute. I'm still pretty raw at Scala so I'm not sure why annotating a sealed abstract class creates a new experimental class.

[srowen]

@hucares I think you can close this PR. As you say in the JIRA, there are no non-Developer non-private APIs in this package.

[mengxr]

I closed this PR. @hucares I'm sorry for not checking the API visibility when I created the JIRA. Please feel free to pick another starter task and I'm happy to walk you through the process of contributing to Spark.