Minor Reporting for Schema Changes

[acmeguy]

Hi,

Here is proposed improvement for error reporting for schema changes when working with hash joins.

This is my first PR so please advise if this is not fulfill Drill requirements for this kid of work or if anything here is sub-par. ( Know the reporting logic could be moved to the exception but I did not want to touch more classes)

Regards, -Stefan

[ilooner]

@acmeguy This would be a nice enhancement. Could you file a DRILL jira and include the jira number in the title of your PR "DRILL-xxxx: Minor Reporting for Schema Changes". Also could you rebase onto the latest master and resolve the conflicts?