Special case Process.exe for PID 0 & 4

Solves issue #528 and #414
Fix the disk_io_counter bug in kernel 2.6 to 2.6.25

In kernel from 2.6 to 2.6.25, /proc/diskstats for subpartitions in
a disk has only 7 fields.
Check this in http://www.mjmwired.net/kernel/Documentation/iostats.txt
Fix the comment space problem.
fix #533: Process.memory_maps() may raise TypeError on old Linux distros
Merge pull request #527 from ddaeschler/master

Fix get_affinity for linux
give CREDIT
Cleaned up syntax
Merge pull request #530 from airekans/master

Fix the disk_io_counter bug in kernel 2.6 to 2.6.25
Merge branch 'master' of github.com:giampaolo/psutil
give CREDIT
Merge pull request #529 from mrjefftang/master

Special case Process.exe for PID 0 & 4
give CREDIT
Merge branch 'master' of github.com:giampaolo/psutil
fix #501: [Windows] disk_io_counters() may return negative values.
last pre-release commit
bump up version
Readme Typo

Given the context, I believe this was referring to [PyPy](http://pypy.org/) not [PyPI](https://pypi.python.org/pypi).
Merge pull request #535 from anthonyryan1/master

Readme Typo