Clearly this is not the right way to fix this; UserDict and MixinDict
ought to be redesigned with the new dict API in mind.  But I'm not
claiming to be in charge of library redesign, I only want zero failing
tests.

(PEP 3106 requires subset comparisons too, those will come later if someone
really wants them. :-)

  and .keys(), .items(), .values() return dict views.

The dict views aren't fully functional yet; in particular, they can't
be compared to sets yet.  but they are useful as "iterator wells".

There are still 27 failing unit tests; I expect that many of these
have fairly trivial fixes, but there are so many, I could use help.

(Not for dict_values, where it can't be done faster than
the default implementation which just iterates the elements.)

One was a modified line that was echoed in an exception;
the other two were softspace problems, fixed clumsily but effectively.

a different feature with the same name).
The change to test_doctest.txt reduces the doctest failures to 3.

old print would suppress the softspace after \t.

* Fix some docstrings and one Print -> print.
* Fix test_{class,code,descrtut,dis,extcall,parser,popen,pkg,subprocess,syntax,traceback}.
  These were the ones that generated code with a print statement.
  In most remaining failing tests there's an issue with the soft space.

converted to "print(x, end=' ')", but other times it must be converted
to "print(x, end='')".  There's no easy way to find out, because it
depends on whether x ends with a newline.  I'm sure I'll find more
like this.

We still have 27 failing tests (down from 39).