misc: Add panic_if / fatal_if / chatty_assert
misc: Add panic_if / fatal_if / chatty_assert

This snippet can be used to replace if + {panics, fatals, asserts} constructs.
The idea is to have both the condition checking and a verbose printout in a single statement.  The interface is as follows:

panic_if(foo != bar, "These should be equal: foo %i bar %i", foo, bar);
fatal_if(foo != bar, "These should be equal: foo %i bar %i", foo, bar);
chatty_assert(foo == bar, "These should be equal: foo %i bar %i", foo, bar);
(transplanted from 9c37adf17edf3366c0a5d13431492879129216ac)

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