Fix warnings in the ant build [LUCENE-5551]

The build produces a lot of warnings. #6194 aims to fail the build on certain warnings, but until we actually eliminate those warnings from the code, failing the build is premature.

This issue is concerned with fixing or suppressing warnings reported by the ant build, anything further than that may need one or more separate issues.

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Migrated from [LUCENE-5551](https://issues.apache.org/jira/browse/LUCENE-5551) by Shawn Heisey (@elyograg), updated May 09 2016
Attachments: [LUCENE-5551-fix-fallthrough.patch](https://apache.github.io/lucene-jira-archive/attachments/LUCENE-5551/LUCENE-5551-fix-fallthrough.patch), [LUCENE-5551-redundant-casts.patch](https://apache.github.io/lucene-jira-archive/attachments/LUCENE-5551/LUCENE-5551-redundant-casts.patch) (versions: 2)
Linked issues:
- #6194

Start by running the Ant build and collecting the warnings described in the issue. Review the attached LUCENE-5551-fix-fallthrough.patch and LUCENE-5551-redundant-casts.patch, and compare the warning policy with linked issue #6194. Done means the reported warnings are fixed or intentionally suppressed without extending the scope beyond the Ant build.

Written by the indexing model from the issue text.