Make changes that allow loglevel and Qunit to be compatible.

1. The first commit demonstrates the issue...which is two-fold, the name 'log' is already taken at the global level by QUnit and the loglevel module incorrectly detects that it's within the CommonsJS environment.

2. The second commit improves the auto-detection of the CommonsJS environment so that it doesn't falsely trigger on QUnit...however, the global 'log' name is still clobbered by QUnit.  Of course at this point it would be easy to reorder the script tags so that loglevel wins...but I think it would be generally useful to be able to adjust the name used by loglevel.

3. The third commit adds an optional ability to specify the name used by loglevel.