Shared lib builder drops package directory

Shared libs that are in packages that also contain python code are stored in `site-packages/foo/bar.so`

PyOxidizer is dropping the `foo` package name, creating conflicts.

A very prominent example is `markupsafe`, `simplejson` and `logbook` all have a `_speedups.so`

```py
>>> import simplejson
import simplejson as json
File "simplejson", line 115, in
File "simplejson.encoder", line 15, in
File "simplejson.encoder", line 12, in _import_speedups
AttributeError: module 'markupsafe._speedups' has no attribute 'encode_basestring_ascii'
```

`tornado` and `websockets` and `fastparquet` all have a `speedups.so`

`cytoolz` and `h5py` and `espressomd` all have `utils.so`, and further nested are `zmq/backend/cython/utils.so` and `yt/analysis_modules/photon_simulator/utils.so`

`dulwich` and `h5py` have `_objects.so`

`xxhash` and `lmdb` have `cpython.so`

`bsdiff4` and `espeak` have `core.so`

`astropy` and `sunpy` have `_compiler.so`

`gevent` and `kivy` both have `_event.so`

PyQt4 and PyQt5 have an almost identical set of built modules under their respective directories.

Cryptodome and Crypto also share a set of similar names.

Third level objects `sklearn/manifold/_utils.so` and `sklearn/tree/_utils.so` probably also have this problem, breaking sklearn even if only it is installed.

Third level objects `gssapi/raw/misc.so` and `samba/dcerpc/misc.so` likely also conflict.

Third level `astropy/stats/_stats.so` and `scipy/stats/_stats.so`

As noted at https://github.com/indygreg/PyOxidizer/issues/167 , brotli and brotlipy both expect `from brotli import _brotli` to import their .so , but that example is a bit messy as the two libraries conflict anyway.

And that is just what I can find in my site-packages :P Obviously there will be many more conflicts I am unaware of.

Start by reproducing the collision with packages such as markupsafe, simplejson, and logbook, then trace the shared lib builder responsible for paths under site-packages. Verify that nested package directories are preserved so same-named .so files remain importable without collisions; the issue names no test or source file, so repository-wide search is required.

Written by the indexing model from the issue text.