Enforce PEP 8 style on Ndiff

Issues fixed:

1       E111 indentation is not a multiple of four
1       E201 whitespace after '['
14      E251 no spaces around keyword / parameter equals
7       E301 expected 1 blank line, found 0
55      E302 expected 2 blank lines, found 1
69      E501 line too long (80 characters)
3       W291 trailing whitespace
4       W601 .has_key() is deprecated, use 'in'