[SPARK-2041][SQL] Correctly analyze queries where columnName == tableName.

Author: Michael Armbrust <michael@databricks.com>

Closes #985 from marmbrus/tableName and squashes the following commits:

3caaa27 [Michael Armbrust] Correctly analyze queries where columnName == tableName.
Use pluggable clock in DAGSheduler #SPARK-2031

DAGScheduler supports pluggable clock like what TaskSetManager does.

Author: CrazyJvm <crazyjvm@gmail.com>

Closes #976 from CrazyJvm/clock and squashes the following commits:

6779a4c [CrazyJvm] Use pluggable clock in DAGSheduler
[SPARK-2025] Unpersist edges of previous graph in Pregel

Due to a bug introduced by apache/spark#497, Pregel does not unpersist replicated vertices from previous iterations. As a result, they stay cached until memory is full, wasting GC time.

This PR corrects the problem by unpersisting both the edges and the replicated vertices of previous iterations. This is safe because the edges and replicated vertices of the current iteration are cached by the call to `g.cache()` and then materialized by the call to `messages.count()`. Therefore no unmaterialized RDDs depend on `prevG.edges`. I verified that no recomputation occurs by running PageRank with a custom patch to Spark that warns when a partition is recomputed.

Thanks to Tim Weninger for reporting this bug.

Author: Ankur Dave <ankurdave@gmail.com>

Closes #972 from ankurdave/SPARK-2025 and squashes the following commits:

13d5b07 [Ankur Dave] Unpersist edges of previous graph in Pregel
SPARK-2043: ExternalAppendOnlyMap doesn't always find matching keys

The current implementation reads one key with the next hash code as it finishes reading the keys with the current hash code, which may cause it to miss some matches of the next key. This can cause operations like join to give the wrong result when reduce tasks spill to disk and there are hash collisions, as values won't be matched together. This PR fixes it by not reading in that next key, using a peeking iterator instead.

Author: Matei Zaharia <matei@databricks.com>

Closes #986 from mateiz/spark-2043 and squashes the following commits:

0959514 [Matei Zaharia] Added unit test for having many hash collisions
892debb [Matei Zaharia] SPARK-2043: don't read a key with the next hash code in ExternalAppendOnlyMap, instead use a buffered iterator to only read values with the current hash code.
[SPARK-2050][SQL] LIKE, RLIKE and IN in HQL should not be case sensitive.

Author: Michael Armbrust <michael@databricks.com>

Closes #989 from marmbrus/caseSensitiveFuncitons and squashes the following commits:

681de54 [Michael Armbrust] LIKE, RLIKE and IN in HQL should not be case sensitive.
Fix DIV and BETWEEN.