Buildout-recipe-isolation

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- Added the ``should-remove-setuptools`` convience setting to remove
setuptools from the isolation.
- Wrote the working set filtering procedure as a funtion. Again, this piece
was not attached to the class's internals.
- Created base classes for the recipes. The first base classes is for a generic
recipe. The other is for the isolators, shared behavior and what not...
- Wrote to write the path file. There was no reason why this needed
to be part of the class.
- Added a pth producer recipe. This recipe does only the pth production part
of the isolation procedure.

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- Added a staging feature. This allows the recipe to build in the final
destinations, but build the isolations within the parts directory.
- Fixed a referencing issue that had to do with the pth file's final location.
- Factored out the usage of the options object within the recipe code.

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- Added this changelog file.
- Fixed the source packaging by adding a manifest file.

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- Initial Release.