zprofile: introduce zprofile use El Capitan (OS X 10.11) introduces a system-level /etc/zprofile which uses a path_helper thing to mangle $PATH. Unfortunately, the way path_helper works, it forces /usr/local/bin and /usr/bin to the *start* of the PATH variable, which means that any PATH mutations I want have to run after /etc/zprofile calls path_helper. As such, move my path insertions into .zprofile{,-machine} rather than .zshenv{,-machine} so that I can still ensure my path entries are at the start of PATH rather than the end. This works because: > Commands are then read from $ZDOTDIR/.zshenv. If the shell is a > login shell, commands are read from /etc/zprofile and then > $ZDOTDIR/.zprofile. Then, if the shell is interactive, commands > are read from /etc/zshrc and then $ZDOTDIR/.zshrc. Finally, if the > shell is a login shell, /etc/zlogin and $ZDOTDIR/.zlogin are read. This means that non-login shells no longer pick up my custom PATH entries, but as I only use OS X as a desktop OS that seems like a workable tradeoff for now.