Fix #235: support for overriding /etc/finit.conf and /etc/finit.d

This change adds support for a new command line option finit.config=PATH
which can be used to tell Finit to start with /etc/factory.conf instead
of /etc/finit.conf.

For the complete experience a new top-level configuration file directive
`rcsd PATH` has aslo been added.  It in turn can be used by factory.conf
as follows to override /etc/finit.d:

    rcsd /etc/factory.d

Manually verified in myLinux

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

doc/cmdline.md

@@ -23,6 +23,16 @@ The `bool` setting is one of `on, off, true false, 1, 0`.
 
   > Note: `<boot/...>` conditions cannot be cleared with `initctl`!
 
+* `finit.config=/path/to/alternative/finit.conf`: override the
+  compile-time bootstrap config file, default:
+
+        ./configure --with-config=/etc/finit.conf
+
+   Useful when starting up in various rescue mode, factory, or
+   production test setups.  Use the top-level configuration file
+   directive `rcsd /path/to/finit.d` to override the default
+   rcS.d directory.
+
 * `finit.debug[=bool]`: Enable finit debug.  This is operated
 	independently of the kernel `debug` setting.  New as of Finit v4.
 

doc/config.md

@@ -10,6 +10,7 @@ Configuration
   * [Hostname](#hostname)
   * [Kernel Modules](#kernel-modules)
   * [Networking](#networking)
+  * [Alternate rcS.d/](#alternate-rcs-d-)
   * [Resource Limits](#resource-limits)
   * [Runlevels](#runlevels)
   * [One-shot Commands (sequence)](#one-shot-commands--sequence-)
@@ -40,6 +41,13 @@ Linux distributions -- each package can provide its own "script" file.
 - `/etc/finit.conf`: main configuration file
 - `/etc/finit.d/*.conf`: snippets, usually one service per file
 
+> **Note:** the above .conf file name and rcS.d directory name are the
+> defaults.  They can be changed at compile-time with two `configure`
+> options: `--with-config=FOO` and `--with-rcsd=BAR`.
+>
+> They can also be overridden from the command line `finit.config=BAZ`
+> and the top-level configuration directive `rcsd /path/to/finit.d`.
+
 Not all configuration directives are available in `/etc/finit.d/*.conf`
 and some directives are only available at [bootstrap][], runlevel `S`,
 see the section [Limitations](#limitations) below for details.
@@ -332,6 +340,27 @@ Debian, Ubuntu, Linux Mint, or an embedded BusyBox system.
 > **Note:** only read and executed in runlevel S ([bootstrap][]).
 
 
+### Alternate finit.d/
+
+**Syntax:** `rcsd /path/to/finit.d`
+
+The Finit rcS.d directory is set at compile time with:
+
+    ./configure --with-rcsd=/etc/finit.d
+
+A system with multiple use-cases may be bootstrapped with different
+configurations, starting with the kernel command line option:
+
+    -- finit.config=/etc/factory.conf
+
+This file in turn can use the `rcsd` directive to tell Finit to use
+another set of .conf files, e.g.:
+
+    rcsd /etc/factory.d
+
+> **Note:** this directive is only available from the top-level
+> bootstrap .conf file.
+
 ### Resource Limits
 
 **Syntax:** `rlimit [hard|soft] RESOURCE <LIMIT|unlimited>`