Warn about split-button dropdowns
Merge pull request #55 from zacechola/btn_dropdown_after_btn

Warn about split-button dropdowns
Check for input-group-* sizing

This checks that .input-group-* sizes are used on .input-group when
.btn-lg, .btn-sm, .input-lg and .input-sm are used within the
.input-group class.

Refs #47
Closes #54 by merging it (after squashing & trivial grammar fix)
Merge branch 'master' into panels

Conflicts:
	dist/browser/bootlint.js
Revert "loosen the selectors."

This reverts commit bf36e3a3ee44bddb181b343b5ed8933422e545bf.

Conflicts:
	dist/browser/bootlint.js
Check for `.panel-collapse`, too.

This reverts back to the original selectors using `.parent()`.

The reason the first version of this ended up failing on the JS docs was
because it was looking for `.parent()` instead of filtering the `.parents()`.
In the JS docs' accordion example, `.panel-body` is wrapped with a
`.panel-collapse` div, so its direct parent wasn't `.panel`.

So I'm wondering if I go back to the original `.parent()` check instead of
the filtered `.parents()`. It'll be much more strict this way, though. But
it also catches the stray `<form>` mentioned in twbs/bootstrap#14300.