replaced tabs with 4 spaces in all python files

PEP 8 (Style Guide for Python Code) suggests the use of 4 spaces:
http://www.python.org/dev/peps/pep-0008/#indentation

If you need to use tools like "git blame", you can use the -w option to
ignore this commit entirely.  Patches will continue to work if you
substitute tabs with 4 spaces everywhere except in the Makefile.
removed all trailing whitespaces
Merge branch 'spaces'