Improve error messages for Hive partition value parsing

Add extra handling for partition value in method HiveClient.toPartition() for issue #1070. It can provide error message with the name of the partition column when any of the parsing functions fail. Attached is the test table and error message.
![test_table](https://cloud.githubusercontent.com/assets/2613617/4932755/b6a57c3a-658d-11e4-901f-a595221717df.png)
![error_message](https://cloud.githubusercontent.com/assets/2613617/4932764/cd56616a-658d-11e4-9038-05d3882337a4.png)


Make the existing function private and rename it to `doParsePartitionValue`, then create `parsePartitionValue` next to it that wraps it to do the exception handling.