[Fix #722] Remove alias_method_chain, use Module#prepend instead

[dalthon]

Ruby 2.0 already have a better alternative to alias_method_chain which is Module#prepend. (Don't remember exactly when introduced).

There is no reason to continue using alias_method_chain, and it was causing some conflicts with other gems.

Checklist

• The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests. (not applicable)
• Added an entry to the changelog if the new code introduces user-observable changes. See changelog entry format for details.