issue-82 - excess options to just warn instead

@twobraids r?

I feel a little bit bad about introducing a new dependency (mock) but it feels like the right thing to do now. 
It's, after all, only a dev requirement. You don't need it for configman to run. 

Also, I'm never getting any peace with this optional configobj dependency. As far as I'm concerned, ConfigParser is so inferior compared to configobj that perhaps it should be a requirement. 

Anyway, note the `x.ini` I added in the test_config_manager.py file. These tests don't work in tox where configobj is not available. When configobj is not available you get this:
```
AllHandlersFailedException: ConfigParser cannot load file: File contains no section headers.
file: x.ini, line: 1
'foo=FOO\n'
```
:(