Exterminate old-style function definitions

Old-style function declarations and definitions (of pre-ANSI C) are harmful.

First and most obvious: they make the compiler spill out lots and lots of unrelated error messages if you forgot to finalize the function declaration with a semicolon. In my experience this happens more often than enough when you copy the signatures out of a .c file into a new .h file.

Second and much more severe: they hide programming errors by making the function accept any argument set, even though the programmer and user most surely did not expect that.