[ESS] completion of colnames with spaces

[Lionel Henry]

> On 25 août 2015, at 21:59, Martin Maechler <maechler using stat.math.ethz.ch> wrote:
> 
> On Tue, Aug 25, 2015 at 7:25 PM, Vitalie Spinu <spinuvit using gmail.com> wrote:
>> 
>> Shouldn't be too difficult to add.
> 
> That sounds great, thank you in advance!
> Note that in this context,  back quotes `abc`  and  double quotes
> "abc"  are equivalent ... just in case one looks easier or more
> logical (font locking?) to implement.

Though backquoting is becoming standard for referring to names because
it's unambiguous (they can never be confused for strings), so I think
we should favour backquotes.

Lionel