Fix #45: add support for rlimit per service/run/task/inetd/tty

This patch extends the existing rlimit implementation to support setting
limits per service, run/task, inetd, and tty.

Use rlimit in /etc/finit.conf to change the global setting, which is
then inherited to each /etc/finit.d/*.conf.  For each .conf file the
rlimit is reinitialized to the global finit.conf settings.

Also, add `unlimited` keyword, to replace the now deprecated `infinity`
keyword.  The latter is however kept, for compatibility with previous
releases, for the foreseeable future.

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

doc/config.md

@@ -51,12 +51,15 @@ Syntax
 * `network <PATH>`  
   Script or program to bring up networking, with optional arguments
 
-* `rlimit <hard|soft> RESOURCE <LIMIT|infinity>`  
+* `rlimit <hard|soft> RESOURCE <LIMIT|unlimited>`  
   Set the hard or soft limit for a resource.  `RESOURCE` is a lower-case
   string matching the `RLIMIT_` constants from `setrlimit(2)`, without
-  the prefix.  E.g. to set `RLIMIT_CPU`, use `cpu`.  The limit is an
-  integer that depends on the resource being modified, see the man page
-  for more information.  The special limit `infinity` means unlimited.
+  the prefix.  E.g. to set `RLIMIT_CPU`, use `cpu`.
+  
+  The limit is an integer that depends on the resource being modified,
+  see the man page, or the kernel `/proc/PID/limits` file, for more
+  information.  Finit versions before v3.1 used `infinity` for
+  `unlimited`, which is still a supported keyword.
 
 ```shell
         # No process is allowed more than 8MB of address space