The 'trace' module logs trace output to stdout, intermingled with regular program output.  This is a problem when you want to read either the trace output or the normal output of the program separately.

To separate the trace output, it could be written to a file or to another file descriptor.

A pull request has been created that fixes this by mimicking bash's behaviour: bash can be told to write trace output to a different file descriptor using the BASH_XTRACEFD shell variable: `exec 42> xtrace.out; BASH_XTRACEFD=42; ...`

Usage of this new feature:

  python -m trace -t -d 111 your_program.py 111> /tmp/your_trace.txt

or:

  t = Trace(count=1, trace=1, trace_fd=1, countfuncs=0, countcallers=0, ignoremods=(), ignoredirs=(), infile=None, outfile=None, timing=False)

Notes:
* `bash -x` sends trace logs to stderr by default; `python -m trace -t` sends them to stdout.  I wanted to change Python to match, but was worried that this might break existing code.  

* Also considered writing trace logs to the file specified with the `-f FILE` option, but worried that it would mess up the count file if `-t` and `-c` were used together.