IDisposable Pattern Cleanup and fix TestDictionary.TestResourceCleanup, #265

[paulirwin]

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Some minor cleanup of IDisposable pattern implementations, and a bug fix.

Fixes #265

Description

I did a review of all implementations of IDisposable.Dispose() to ensure they follow the Dispose Pattern correctly, and someone had clearly already done all of the hard work here: it was nearly all done right. There were a couple cases that I fixed in this PR:

• Lucene42DocValuesConsumer.SortedSetEnumerator did not implement the pattern correctly, but it also is an internal type with no subclasses, so this was made sealed.
• Hunspell's TestDictionary.CloseCheckInputStream had a curious shadowing of Dispose that was causing it to not work correctly, and this exposed a bug: the stream wrapper was getting disposed of in Hunspell.Dictionary, when it is expected to not be disposed of. The shadowed Dispose method was never called, even if the Dictionary code actually did dispose of the wrapper. This created a false negative, where the test thought it wasn't disposed of when it actually was. This PR fixes that by removing the shadowing Dispose method, marking this.disposed in the actual Dispose pattern override method so that it's properly marked when called virtually, and leaving the stream open in the Dictionary.ReadDictionaryFiles method to match Java's behavior (and the expected behavior per the unit test).