[SPARK-5775] [SQL] BugFix: GenericRow cannot be cast to SpecificMutableRow...

[SPARK-5775] [SQL] BugFix: GenericRow cannot be cast to SpecificMutableRow when nested data and partitioned table

This PR adapts anselmevignon's #4697 to master and branch-1.3. Please refer to PR description of #4697 for details.

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Author: Cheng Lian <lian@databricks.com>
Author: Cheng Lian <liancheng@users.noreply.github.com>
Author: Yin Huai <yhuai@databricks.com>

Closes #4792 from liancheng/spark-5775 and squashes the following commits:

538f506 [Cheng Lian] Addresses comments
cee55cf [Cheng Lian] Merge pull request #4 from yhuai/spark-5775-yin
b0b74fb [Yin Huai] Remove runtime pattern matching.
ca6e038 [Cheng Lian] Fixes SPARK-5775