Trivial lint fixes
More precise condition checking
Remove undefined variable

This doesn't appear to be used or defined anywhere. Removing it
makes sorting (by clicking on column headers) work again.
Clearly a typo

This clone function would have never used its overwrites param...
Remove dead code

This expression doesn't refer to anything.
Exclude unwanted properties from the prototype
Add a jshint config file for the project

Hopefully some day most of the options in the top section can be
turned on :)
Improve logic to avoid returning an assignment
Silence warnings about missing new with constructors

The add-on SDK doesn't use new for any of these so it's probably
better to follow their guidance and turn off this warning.
Turn off warning about a possible strict violation
Merge pull request #585 from fmarier/fix_lint_notices

Fix lint notices