Use stable Jedi from PyPI
Fix: elpa target in Makefile
No need to clean .cask/*/elpa in test-all

Thanks to cask installing packages in separate directories.
Remove all cask environments by "make clean"
Use marmalade to install eieio in emacs23

See also: https://github.com/cask/cask/pull/38
Use both cassou and ubuntu-elisp PPA

It looks like ~ubuntu-elisp and ~cassou provides different
versions (daily vs bimonthly) so it makes sense to try both.

See:
- https://github.com/cask/cask/issues/172
- https://launchpad.net/~ubuntu-elisp/+archive/ppa/
- https://launchpad.net/~cassou/+archive/emacs
Show stdout/err during "cask install" using tee

This makes .travis.yml less complex.  As travis-ci.org hides error
during installation step, there is no reason to have manual
after_failure anymore.
Fix allow_failures in .travis.yml
No need to install emacs-snapshot-gtk
Run "make elpa" via "make before-test"

This completes 32538392ad7191b10a1653b1f6823063e9ee8691
Do not store install.log for "cask install"

... so that make notices exit status of "cask install".

This is to avoid error like this:
https://travis-ci.org/tkf/emacs-jedi/jobs/19448211#L493
Merge branch 'fix-travis'