[ESS] iESS - consistent string formatting within single and double quotes

[Vitalie Spinu]

> No, no.. We really won't go there; long time ESS users already
> know the pain we occasionaly have from treating `back quotes` as
> something to be fontified in pairs and how ugly the *R* buffer
> gets messed up, when R or C code called from R puts out messages
> quoted `like' that...
>

Back-quote is really annoying actually. It often happens with
install.package and roxigenize to me. And I don't know an easier
solution than typing #` at R prompt.

May be a  way to deal with it is to match `string' withing a single
line only, most of backquoted strings are short anyhow.

Vitalie.