[SPARK-4052][SQL] Use scala.collection.Map for pattern matching instead of using Predef.Map (it is scala.collection.immutable.Map)

Please check https://issues.apache.org/jira/browse/SPARK-4052 for cases triggering this bug.

Author: Yin Huai <huai@cse.ohio-state.edu>

Closes #2899 from yhuai/SPARK-4052 and squashes the following commits:

1188f70 [Yin Huai] Address liancheng's comments.
b6712be [Yin Huai] Use scala.collection.Map instead of Predef.Map (scala.collection.immutable.Map).