For normal usage this change should be a NOOP. However it enables the
use case where the user might want to predefine what session gets
connected to when the shell is launched. Running `zsh` will still net
you a connection to the last used tmux session or a new one named
"zprezto" if none exists. However `env tmux_session=myname zsh` will
connect you specifically to a session called 'myname' including creating
it if it doesn't exist.
This is particularly useful in window managers where a key binding might
open a terminal with a predefined session or even show a list of current
sessions and open a new terminal connected to that session.
The default session name may still be set using zstyle as documented.
Setting the auto-start 'remote' and 'local' zstyles for the screen and
tmux modules to 'true' automatically starts a session in SSH connections
and in local terminals respectively.
Signed-off-by: Sorin Ionescu <sorin.ionescu@gmail.com>
