Various updates to the FileDiff class.
Various updates to the FileDiff class.

* bindings/swig/python/svn/fs.py:
  (FileDiff.either_binary): new method to detect whether either file
    is a binary file, thus indicating whether the diff should be skipped
  (FileDiff.get_pipe): use a list for the diff command, along with the
    popen2 module (rather than os.popen). this avoids the shell for
    security purposes, and allows spaces in file names.
  (FileDiff.__del__): ignore errors while trying to remove the files.

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion