Update the SWIG bindings docs.

* subversion/bindings/swig/INSTALL
  Run 'make' in the 'build' tree, not the 'source' tree. Split the 'testing
  and using' section into separate sections. Expand the 'using' section for
  Python.

* subversion/bindings/swig/python/README
  Write better code examples.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1445801 13f79535-47bb-0310-9956-ffa450edef68