Add a |python| wrapper script which sets the right environment variables and invokes /data/python/bin/python.

Crucially, the wrapper script sets LD_PRELOAD=libpython2.7.so.  Without
this, we can't load any of the libs in lib-dynload, which means that we
can't import any Python module which uses native code (e.g. the select
module).

Without LD_PRELOAD, we get an error like the following when we try to
import a module which uses native code:

  >>> import subprocess
  Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/data/python/lib/python2.7/subprocess.py", line 429, in <module>
    import select
  ImportError: Cannot load library: reloc_library[1285]:  9814 cannot locate 'PyDict_Next'...

The root problem is that the lib-dynload libraries do not have an
explicit dependency on libpython.so (see readelf -d), so therefore the
bionic linker doesn't try to resolve their symbols against libpython.
Setting this dependency would be the Right Fix.
Don't nuke the LD_LIBRARY_PATH and LD_PRELOAD variables.

You might want to pass an LD_LIBRARY_PATH to a child process of python, for example.
Merge pull request #1 from jlebar/wrapper-script

Add a |python| wrapper script which sets the right environment variables...