Add lang/pypy-devel for non-stable releases of PyPy.
pypy-devel is intended as a staging ground for beta releases and - while
no beta releases are available - snapshots of pypy default branch.
While introducing pypy-devel to build logic has been reworked to better
accomodate pypy3. The lib-python/2.7 and lib_pypy folders are not renamed
after extraction (with only symbolic links used to emulate the structure).
PyPy still expects the standard structure and the symbolic links satisfy
The devel port was requested by mva@ to better support commercial clients.