Supporting relative/absolute Images paths

I'm not a regexp expert but i tried adding support for those kinds of paths :

/img/file.png
./img/file.png
../img/file.png

By moving one "/" inside the optional "http" part of the regexp, and adding "(?:.){0,2}".
It works fine and doesn't seem to break anything as far as i know.

If anyone is interested, i needed this in order to work with CKEditor and KCFinder image upload/insertion.