ignore autogenerated __init__.py files

[fwyzard]

ignore autogenerated init.py files

[Dr15Jones]

Ignoring all init.py files isn't safe since we do have a few legitimate ones such as
PhysicsTools/PythonAnalysis/python/init.py
PhysicsTools/PythonAnalysis/python/rootplot/init.py

[ktf]

I discussed this with @fwyzard privately. .gitignore affects only untracked files, not tracked ones, so this only affects new legitimate __init__.py files which would have to be added explicitly via git add -f.

Between CMSSW_5_2_0 and CMSSW_7_0_0_pre0 (i.e. almost last two years) we had only 12 __init__.py files modified, in 11 cases it was automatically generated files being removed, in one case it was a one line modification (which the change in question would still allow as usual) and there were no cases in which a new __init__.py file was added. Between CMSSW_7_0_0_pre0 and CMSSW_7_0_0_pre2 (i.e. last two months) I could count already 2 __init__.py added by accident in a pull request (most likely via git add .). I think it's safer the setup Andrea proposes.

In any case once we move to generate files in a separate path, we can revert this.