When this option is used, the child process in the new terminal
instance will inherit its environment from the footclient process,
instead of the foot server’s.
Implemented by sending (yet another) dynamic string list as part of
the client -> server setup packet. When the new option is *not* used,
the setup packet is now 2 bytes larger than before.
On the server side, the slave process now uses execvpe() instead of
execvp(). There’s plumbing to propagate a new ‘envp’ argument from
term_init() all the way down to slave_exec(). If ‘envp’ is NULL, we
use ‘environ’ instead (thus matching the old behavior of execvp()).
Closes#1004
* Rename user_warning to user_notification
* Add warning and error types (in addition to the existing deprecated)
* Simplify logic when emitting a user notification after forking; we
don't need to copy the notification data since we're in a new
process and have total control over that memory.
This is used when spawning the slave, to set its current working
directory just before we exec() the client.
In a regular foot instance, we set the cwd from getcwd().
In a foot server instance, each connecting client sends its cwd to the
server, and we use that.
