Major change, rename <svc/...> conditions to <pid/...> conditions

The <svc/foo> condition was created to synchronize starting services,
hence the abbreviation.  Example: the Quagga ripd needs to start after
the zebra daemon to ensure its UNIX domain socket is active, otherwise
events may be lost.

However, considering that synchronization was implemented with UNIX PID
files, e.g. waiting for /var/run/quagga/zebra.pid to be created, the
condition abbreviation name <svc/foo> was hard to understand by most
newcomers to Finit.  To make matters worse, a new feature to track or
even create PID files for services that don't create one themselves,
using the syntax 'pid:/path/to/foo.pid' was added.

Connecting the dots between these wasn't obvious.

This patch renames service conditions pid conditions and also adds
a compatibility wrapper to the Finit .conf parser.  Any condition
given in old .conf files with 'svc/' prefix are internally renamed
'pid/', along with a LOG_INFO notice in syslog.

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

plugins/pidfile.c

@@ -323,7 +323,7 @@ static struct context pidfile_ctx;
  *
  *     service <net/iface/lo> /sbin/dropbear ...
  *
- * Which provides the <svc/sbin/dropbear> condition, will not be
+ * Which provides the <pid/sbin/dropbear> condition, will not be
  * set by pidfile.so during `initctl reload` because dropbear is
  * still SIGSTP:ed waiting for <net/iface/lo>.
  */