[SPARK-7718] [SQL] Speed up partitioning by avoiding closure cleaning

According to yhuai we spent 6-7 seconds cleaning closures in a partitioning job that takes 12 seconds. Since we provide these closures in Spark we know for sure they are serializable, so we can bypass the cleaning.

Author: Andrew Or <andrew@databricks.com>

Closes #6256 from andrewor14/sql-partition-speed-up and squashes the following commits:

a82b451 [Andrew Or] Fix style
10f7e3e [Andrew Or] Avoid getting call sites and cleaning closures
17e2943 [Andrew Or] Merge branch 'master' of github.com:apache/spark into sql-partition-speed-up
523f042 [Andrew Or] Skip unnecessary Utils.getCallSites too
f7fe143 [Andrew Or] Avoid unnecessary closure cleaning