bug#13563: tabulated-list-print-col nicer help-echo

[Glenn Morris]

Version: 24.4

Jonas Bernoulli wrote:

>>> * If the label already has a help-echo property then use that help-echo
>>>   instead of overriding it with a generic one.  This allows displaying
>>>   additional information when it makes sense.

I applied this part, thanks.

> One other thing I forgot to include in this pull request: I think it
> would make sense to set `x-stretch-cursor' to nil in
> `tabulated-list-mode'. 

I don't see the point.

> One shouldn't set that to t globally (I did for a while, silly me) but
> it also does not hurt to actively override such a setting in cases
> where it is known not to make any sense.