AVL Tree in ImmutableList not always balanced after insert

[PatrickMcDonald]

When Insert is called in ImmutableList, the list is not always balanced correctly by the MakeBalanced method. This was exposed PR dotnet/corefx#67. I have created a minimal test which exposes this bug and will create a separate PR to correct this.

[AArnott]

@PatrickMcDonald Can you please revise your commit message to conform with the format described here?

In particular, we want the first line to be a description of the actual change (80 chars or less) followed by a blank line and additional paragraphs as necessary. Your last line can be "Fixes dotnet/corefx#103" so that github associates the the commit with the issue.

You can revise your commit using git commit --amend and then doing a forced push to your branch.

[forki]

This wasn't merged but closed by a bot?
Is this correct?

[PatrickMcDonald]

@forki Issue was closed, but PR was merged