[SPARK-7267][SQL]Push down Project when it's child is Limit

[pzzs]

SQL

select key from (select key,value from t1 limit 100) t2 limit 10

Optimized Logical Plan before modifying

== Optimized Logical Plan ==
Limit 10
Project key#228
Limit 100
MetastoreRelation default, t1, None

Optimized Logical Plan after modifying

== Optimized Logical Plan ==
Limit 10
Limit 100
Project key#228
MetastoreRelation default, t1, None

After this, we can combine limits

[rxin]

Jenkins, test this please.

[SparkQA]

Test build #31367 has finished for PR 5797 at commit dc83ae9.

• This patch fails Spark unit tests.
• This patch merges cleanly.
• This patch adds no public classes.
• This patch does not change any dependencies.

[scwf]

Retest this please

[rxin]

Jenkins, test this please.

[SparkQA]

Test build #31396 has finished for PR 5797 at commit 70d0fca.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.
• This patch adds the following new dependencies:
  • jaxb-api-2.2.7.jar
  • jaxb-core-2.2.7.jar
  • jaxb-impl-2.2.7.jar
  • pmml-agent-1.1.15.jar
  • pmml-model-1.1.15.jar
  • pmml-schema-1.1.15.jar
• This patch removes the following dependencies:
  • activation-1.1.jar
  • jaxb-api-2.2.2.jar
  • jaxb-impl-2.2.3-1.jar

[rxin]

Thanks. Merging in master.