#511 secret undocumented switches to counter::get

[Michael Schlenker]

counter::get has several switches that are not
documented, but sound useful -maxPerMinute,
-maxPerHour, -maxPerDay

Those throw an error for non time based counter types:
(bin) 70 % counter::init foo -hist 20
(bin) 71 % counter::get foo -maxPerMinute
can't read "counter(maxPerMinute)": no such element in
array

if they get exposed, throw a more helpful error message