Add window_cached decorator for ctrlp segment
Make nerdtree segment use bufvar_exists
Add functional tests for plugin themes
Add jobnum segment to default_leftonly theme
Fix copy-paste typo in shell.py
Add bash functional tests
Add a few empty lines, rename bash directory to 3rd
Use get_output function
Replace zyx-desktop with HOSTNAME
Move shell testing to tests/test_shells/test.sh
Made it use screen for testing
Move tests/test_shells/input.sh to tests/test_shells/input.bash
Add zsh functional tests
Also install screen
Run apt-get with sudo and -qq like suggested in travis documentation

Documentation though suggests using before_install. Not sure why.
Add missing zsh.ok
Also replace $USER with USER
Replace sed with python script

sed escaping is wrong: e.g. re.escape() will escape `+`, but with BRE escaped 
plus is quantifier
Always show hostname (travis is ssh), fix jobnum in zsh
Merge pull request #747 from ZyX-I/more-functional-tests

More functional tests