Update filetype plugin

[dmitrivereshchagin]

• Add header
• Replace 're' with 'regexpengine'
• Simplify patch check

[bounceme]

should we add a undo_ftplugin variable?

[bounceme]

maybe also make the iskeyword setting be set in the ftplugin if the vim version is too old

[dmitrivereshchagin]

Yes we should. But to make it work one of the following should be done

• provide full filetype plugin which set b:did_ftplugin variable
• move current filetype plugin to after/ftplugin directory

In other cases filetype plugin bundled with Vim will override b:undo_ftplugin.