Improve synchronization in MOPClassLoader and JavassistByteCodeStubBuilder

[activeeon-bot]

Original issue created by Laurent Pellegrino on 26, Feb 2015 at 17:34 PM - PROACTIVE-1392

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The purpose is to investigate if the synchronization in MOPClassLoader and JavassistByteCodeStubBuilder classes could be improved (e.g. finding a pattern to apply) so if any new method is added in one of these classes lock acquisition can not be forgotten.

[laurentpellegrino]

For instance, make use of read/write locks instead of synchronized blocks.