Bugfix for the issue #109: Fails to properly parse NOSE_COVER_PACKAGE environment variable.
Now the following line works correctly:

os.environ['NOSE_COVER_PACKAGE'] = 'package1,package2,package3'
Suppress tracebacks caused by ConfigErrors.

Show a kind error message instead of a traceback
when an unknown configuration variable is found in
a file.
Use `nose.__loader__` to load 'usage.txt', if available.

Previously we only used `nose.__loader__` if we thought
that the loader was zipimporter. Additionally, we use
`nose.__file__` to build the path to 'usage.txt' as
suggested by PEP-302.
Merge pull request #572 from bfroehle/loader_usage_txt

Use `nose.__loader__` to load 'usage.txt', if available.
Merge pull request #528 from andrea-corbellini/master

Suppress tracebacks caused by ConfigErrors
Add a test for #109: Fails to properly parse NOSE_COVER_PACKAGE.

This also provides a place to do more testing of the coverage plugin.
Merge pull request #520 from Bahus/patch-1

Bugfix for the issue #109: Fails to properly parse NOSE_COVER_PACKAGE
environment variable.  Also added a test.

Note: I did not merge the other patch on this branch (ffc3701) because
I'm not sure it's the right fix.