Remove underline option

This code will not work with the customization interface, and will
potentially mess up theming. Instead, leave the user to modify his own faces.
Don't invade the term-* namespace
Prefer derived-mode-p to string= check of major-mode
Remove -version var, which only causes confusion in the package.el world
Prefer "when" to "if" when there is no "else" form
Merge pull request #1 from purcell/master

Misc fixes