631 ("line is too long"): set column according to start

[blueyed]

This changes the column for "line is too long" warnings to the start
of the too long text.

[mpeterv]

I like this, if an editor plugin highlights warning ranges in code this should make it clear where an overly long line should have ended to pass the check. Thanks!

[blueyed]

@mpeterv
Exactly my use case: I've noticed this with the luacheck integration in Neomake, and thought it's best to fix it upstream (instead of adjusting it later based on the message).
Thanks for merging it, and this nice linter in the first place!