This means that dbus-daemon will log something like

    dbus-daemon[123]: Unable to add reload watch to main loop

to syslog and/or stderr according to its configuration, while other
libdbus users will print something like this to stderr:

    dbus[4567]: arguments to dbus_foo() were incorrect, assertion
    "connection != NULL" failed at file dbus-foo.c line 123.
    This is normally a bug in some application using the D-Bus library.

This slightly changes the meaning of the argument to _dbus_warn()
and _dbus_warn_check_failed. Previously, a trailing newline was
expected, and a missing newline would have resulted in incorrect
output. Now, a newline is supplied automatically by the
library (like g_warning()), and messages that end with a newline will
result in an unnecessary extra newline in output.

This extra newline is harmless, so I'm not going to change all the
callers immediately.

Signed-off-by: Simon McVittie <smcv@debian.org>