Support multiple paths for shared parts
Use a new option buildout:shared-path-list that is now a new line separated list of path, only the last part is used to install new parts, other are read-only.
Also some cleanups in the test suite.
Use a new option buildout:shared-path-list that is now a new line separated list of path, only the last part is used to install new parts, other are read-only.
Also some cleanups in the test suite.