AVRO-2117: Code cleanup

[Niels Basjes <Ni...@basjes.nl>]

Hi,

Merry X-Mas to you all.


When there are a lot of warnings that are 'trivial' they tend to hide the
warnings that are important.
So in most projects I aim for a 'zero warning' situation so you can spot
any problem in de code base much faster.


I recently put some effort into cleaning up some of the simple and needless
warnings that various tools give on the current codebase. This is not 'all
warnings' but it is a big step in the right direction.

https://issues.apache.org/jira/browse/AVRO-2117
https://github.com/apache/avro/pull/266
To keep an overview of what was changed I used a single commit per "type of
fix".

I would really appreciate feedback from you guys if and how to proceed with
this one.

Thanks.

-- 
Best regards / Met vriendelijke groeten,

Niels Basjes