do ProtocolEvents fixing only when there is required fields missing in the requested schema

https://issues.apache.org/jira/browse/PARQUET-61
This PR is trying to redo the https://github.com/apache/incubator-parquet-mr/pull/7

In this PR, it fixes the protocol event in a more precise condition:
Only when the requested schema missing some required fields that are present in the full schema

So even if there a projection, as long as the projection is not getting rid of the required field, the protocol events amender will not be called.

Could you take a look at this ? @dvryaboy @yan-qi
spaces around the else