Allow W117 and unused to be toggled per line.

This patch allows JSHint to apply `-W117` and `unused:false` to a local part within the file.

Use-case: I have code where some variables are only defined if some conditional is true. I don't want to put `/* globals name_of_variable */` in the file, because it could result in unknowingly using the variable when it does not exist. Therefore I need an option to toggle the error for a specific section.