Fix the gevolution plugin.

This pulls the patches from PIDGIN-15353 (Ed Catmur) and
https://bugs.gentoo.org/526644 (Lars Wendler) to fix everything.

Testing Done:
Loaded the plugin and verified that configuration worked. I don't have any good accounts to actually sync with evolution so I didn't try that part but gentoo has been carrying the patch from PIDGIN-15353 for very long time.

Bugs closed: PIDGIN-15353

Reviewed at https://reviews.imfreedom.org/r/610/