bug#40137: 25.1; ERC ignore function should allow specifying a limited duration

[Lars Ingebrigtsen <larsi@gnus.org>]

Lars Ingebrigtsen <larsi@gnus.org> writes:

> So just upcase and add a P to the start and we're there.  :-)

It was a bit more work, and time specs are ambiguous (1m means a month
or a minute?), but I've now implemented this.

The ambiguousness means that this could probably be tweaked a bit, but I
made the prompting thing into its own function, and we can more it to a
more central location if something else wants to use it.  And then tweak
further, if necessary.  For instance, one may do a DWIM check on the
string:  1m4m clearly means 1 month and four minutes and 2d4m means two
days and four minutes, while 1y1m is terminally ambiguous.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no