Fix "make install" of Python.  Remove old code and restructure the Python sources under lang/python to simplify the installation step.

--HG--
rename : lang/python/fpacking.py => lang/python/wiredtiger/fpacking.py
rename : lang/python/intpack-test.py => lang/python/wiredtiger/intpack-test.py
rename : lang/python/intpacking.py => lang/python/wiredtiger/intpacking.py
rename : lang/python/packing-test.py => lang/python/wiredtiger/packing-test.py
rename : lang/python/packing.py => lang/python/wiredtiger/packing.py
Merge pull request #598 from wiredtiger/python-install

Fix "make install" of Python.
Pass any configured Python prefix through to the Python install step.