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>

src/service.c

@@ -825,7 +825,7 @@ static void parse_cmdline_args(svc_t *svc, char *cmd)
  * special case when a service is declared with <!> means it does not
  * support SIGHUP but must be STOP/START'ed at system reconfiguration.
  *
- * Service conditions can be: svc/<PATH> for PID files, net/<IFNAME>/up
+ * Service conditions can be: pid/<PATH> for PID files, net/<IFNAME>/up
  * and net/<IFNAME>/exists.  The condition handling is further described
  * in doc/conditions.md, but worth mentioning here is that the condition
  * name itself can be modified using the :ID and name:foo syntax.