__init__.py doesn't always get installed

[asylvest]

Still having intermittent issues with this... one theory I have is that in build.py's python_package(), nod.sig doesn't end up being unique when there are multiple Python modules because all of the __init__.py files are empty. I had a point where I was trying to explicitly do waf install --target=python_init_file_coda and it wouldn't do anything. Then I changed the nod.sig value to something unique and this worked. But... the chaining still didn't: the module I was trying to install directly still didn't connect the python_init_file_coda target like it should have itself.

I wonder if we should just be creating this empty file once at configure time. Then both the configure and build steps would be simpler... you wouldn't need the special python_package feature.

@chvink no need to work this right this second but keep it in the back of your head

@clydestanfield @apakanati @JonathanMeans