Added some extra python stuff

Hi,

Great work with the buildroot, I added some extra stuff in my fork useful for my robot toying:

Greenlet
gevent
Wiringpi2

Also a quick dirty  fix for systemd not compiling because execvpe is now included in busybox:

package/systemd/systemd-uclibc-z-execvpe-patch.patch

If you find the useful it should merge without issues.

Regards,

-R