CODING_STYLE: document that we don't break lines at 80ch
util: change return value of startswith() to non-const

This way we can use it on non-const strings, and don't end up with a
const'ified result.

This is similar to libc's strstr() which also takes a const string but
returns a non-const one.
util: simplify close_nointr() a bit
util: make asynchronous_close() really work like an asynchronous version of safe_close()

Save/restore errno, like we do in safe_close(). And don't fork a thread
if the parameter is already negative.
core: unify how we generate the prefix string when dumping unit state
service: asynchronous_close() already checks for negative parameters, no need to duplicate that
service: remove some pointless linebreaks, to make things more readable
service: don't invoke functions at the same time as declaring variables
service,strv: introduce strv_find_startswith() and make use of it

Unlike strv_find_prefix() the new call will return a pointer to the
suffix of the item we found, instead of the whole item. This is more
closer inline with what startswith() does, and allows us to simplify a
couple of invocations.
manager: reuse sockaddr_union instead of redefining our own version of it
manager: don#t dispatch sd_notify() messages and SIGCHLD multiple times to the same units
core: allow informing systemd about service status changes with RELOADING=1 and STOPPING=1 sd_notify() messages
notify: send STOPPING=1 from our daemons
update TODO
bus: when terminating our bus-actviated services that exit-on-idle send STOPPING=1 via sd_notify()

This should fix a race where a service thatis idle drops its name, and
is immediately requested by another client, which causes dbus-daemon to
ask systemd to activate it again, but since systemd still assumes it is
running it won't do anything.
execute: explain in a comment, why close_all_fds() is invoked the second time differently