argcheck: a module to check argument ranges

This code provides some macros to check arguments for valid value ranges.
Consider this a mild version of assert(3), because all it does is to log
a message and continue.

These macros don't replace error handling, but they are useful in
situations where an error is unexpected but not common, i.e.
this shouldn't happen but if it does let me know".

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>