BREAKING: Lucene.Net.Index.IndexWriter: Fixed Dispose(waitForMerges) vs Dispose(disposing)

[NightOwl888]

See #265.

Fixed Dispose() overloads so there is no method signature conflict between the public Dispose(waitForMerges) method and the protected Dispose(disposing) method which is meant for end users to override. This was done by adding a protected virtual void Dispose(bool disposing, bool waitForMerges) overload and removing virtual from the public Dispose(bool waitForMerges) overload.

This may break some existing code that either

1. Subclasses IndexWriter and overrides the public virtual void Dispose(bool disposing) method. Instead, the subclass should override protected virtual void Dispose(bool disposing, bool waitForMerges).
2. Subclasses IndexWriter and implements a finalizer, in which case the call should now call Dispose(disposing: false, waitForMerges: true). Previously, finalizers were not supported because there was no Dispose() overload to call to pass the disposing parameter.