Remove SwigPyObject_print and SwigPyObject_str, and make the generated wrapper use the default python implementations, which will fall back to repr (for -builtin option).

Advantages:
- it avoids the swig user having to jump through hoops to get print to
  work as expected when redefining repr/str slots.
- typing the name of a variable on the python prompt now prints the
  result of a (possibly redefined) repr, without the swig user having to
do any extra work.
- when redefining repr, the swig user doesn't necessarily have to
  redefine str as it will call the redefined repr
- the behaviour is exactly the same as without the -builtin option while
  requiring no extra work by the user (aside from adding the
%feature("python:slot...) statements of course)
- the patch simplifies pyrun.swg a tiny bit.

Disadvantage:
- default str() will give different (but clearer?) output on swigged
  classes compared to unpatched swig

SF Bug #326