Ensure old- and new-style Python APIs can coexist in the same process

[martyngigg]

At the moment if you try and import the new mantid package and the old MantidFramework in to the same process you get a boost assertion error that some registrations already exist and the program exits.

The issue is that boost::python's type conversion registry is a static map and is shared among all dynamically loaded extension modules. The solution is to statically link the old API to boost python so that it gets a private copy of the registry and they don't clash.

We don't want to statically link the new one however as we have split modules that need to share the registry.

[martyngigg]

This issue was originally trac ticket 4204