pytest-xdist-1.11.ebuild: Fix '~x64' -> '~x86' typo
pytest-xdist-1.11.ebuild: Add py >= 1.4.22 dependency

The requirement was added (with an pre-release py version) in
pytest-xdist's b8195374 (depend on latest py dev version to support
"--boxed" properly, 2014-07-05 [1]), just before they cut 1.11.

[1]: https://bitbucket.org/hpk42/pytest-xdist/commits/b8195374a4aa758a5f09562acd4d669d9f53cad8