Update pypi2spec.spec

1. Use install -m to remove executable bits directly.
2. Use %__python2 macro instead of %__python to avoid mess after moving to Py3 stack.
3. Use more standardized macro for python 2.x package.
4. Remove obsoleted lines.
5. Small cleanup of English.
Update pypi2spec.spec

Add changelog per comment.
Merge pull request #18 from cicku/master

Update pypi2spec.spec