trace.c
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History
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26th October 1992  J R C  Started

   This is a simplified version of various other tracing modules that have
been written at various other times.

    It only provides one function, |trace_f|, which takes a file name, a
line number and a |printf|-like argument line, and sends them to the tube.

   Trace.h also includes a macro |tracef| that expands to |trace_f| after
inserting |__FILE__| and |__LINE__| as the first two arguments. In order to
use this, commas cannot be used to separate the arguments, since they cause
the macro preprocessor to count the arguments as separate. Instead, use

      #define _ ,

and use |_| to separate the arguments.
