Replace pythonz with pyenv

Depending on Python to manage Python is silly.
Add utility aliases for Cygwin

Signed-off-by: Sorin Ionescu <sorin.ionescu@gmail.com>
Remove duplicate alias definitions
Simplify a conditional
Do not define $GEM_HOME

Defining it breaks gems for all users who neither use RVM nor rbenv,
but have a different default Ruby version nonetheless.

Signed-off-by: Sorin Ionescu <sorin.ionescu@gmail.com>
Use correct option for pacman search aliases
Stop module loading when external code fails to source
Comment an unnecessary style
update completion external stuff
Merge branch 'master' of github.com:sorin-ionescu/prezto

Conflicts:
	modules/pacman/init.zsh