_JavaArrayClass handles Python 3 (complex) slices

* __get/setslice__ have merged with __get/setitem__ in Python 3
* Added Python-side support for complex slices (reversed, stepped, ...)
Ignore files generated during tests
Tests ported to Python 3

- ... using 2to3
- dict JProxy() parameter changed to dictionary
- build.xml : changing Java version from 1.4 to 1.6 (avoids a Java compilation error)
Updated README file: tests have been ported to Py3