[Click] ICMPPingSource: add warning when interval parameter is set in pull context

[Bart Braem]

Hi all,

We noticed that the ICMPPingSource will ignore the interval parameter if used in a pull context. We completely understand why, however our students were quite confused. That's why I sent a pull request at <https://github.com/kohler/click/pull/37> to add a warning.
It's my first pull request on github, so suggestions for improvements are welcome :-)

best regards,
Bart
-- 
Bart Braem
PATS research group - IBBT
Dept. of Mathematics and Computer Science
University of Antwerp
Campus Middelheim, G3.26
Middelheimlaan 1
B-2020 Antwerpen, Belgium
Phone: +32 (0)3 265.38.64
Fax: +32 (0)3 265.37.77
Web: www.pats.ua.ac.be