Traces FUNCTION with trace output going to BUFFER.
For every call of FUNCTION Lisp-style trace messages that display argument
and return values will be inserted into BUFFER. This function generates the
trace advice for FUNCTION and activates it together with any other advice
there might be!! The trace BUFFER will popup whenever FUNCTION is called.
Do not use this to trace functions that switch buffers or do any other
display oriented stuff, use `trace-function-background' instead.
To untrace a function, use `untrace-function' or `untrace-all'.
(fn FUNCTION &optional BUFFER)