conf: add provides, additional conditions a service supplies

A block title is a service identity, so two variants of one service
gated differently per platform cannot share a title.  They do need to
share the barrier condition downstream services wait for, which until
now was spelled by the identity alone and so could not be shared:

    service syslogd:udev {
        if         = "udevd"
        conditions = { "run/udevadm:5/success" }
        provides   = "pid/syslogd"
        command    = "-syslogd -F"
    }

Any namespace is allowed, since the point is publishing a name that
existing configurations already wait on.  A claim on a condition that
is already owned is dropped with a warning naming the owner, and the
service still registers: the overlap is a configuration bug, and an
init system is more useful degraded than refusing to boot.  A real
identity outranks a claim, pid/<ident> is how Finit tracks its own
services, so it is not up for grabs.

Claims are dropped before each reload re-reads the .conf files.  Doing
it per service as it re-registers is not enough, since services are
read in file order and one re-registering would lose to a claim
another had not dropped yet, flipping the owner on every reload.

initctl cond dump asked who owned a condition only for the pid/
namespace and printed 'static' for usr/, which now hides a provider.
It asks first and falls back to what the namespace implies.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

src/service.c

@@ -2391,6 +2391,7 @@ svc_t *service_register(int type, char *cfg, struct rlimit rlimit[], char *file)
 		svc->dir_mode[i] = 0755;
 	}
 	svc->dir_preserve = SVC_DIR_PRESERVE_NO;
+	svc->num_provides = 0;
 
 	if (!svc_is_tty(svc) && ctty) {
 		char *dev = ctty;