ref-manual, dev-manual: Updates to support recipe-specific sysroots

Changes covered several areas.  Version 2.3 of the YP now supports
recipe-specific sysroots and is not limited to machine-specific
as was prior releases.  Manual changes were as follows:

dev-manual: "Sharing Files Between Recipes" - Wordings were changed
to support the new functionality.

ref-manual: do_prepare_recipe_sysroot task added to the list of
tasks described in "Configuration and Compilation".

ref-manual: Extensive re-write of the "staging.bbclass" section.

ref-manual: Added a section to the build structure for
build/tmp/work/tunearch/recipename/version/.  This section breaks
down the recipe-specific subdirectories used to create (stage)
the sysroot.

ref-manual: New section (entry) for the do_prepare_recipe_sysroot
task in the task chapter.

ref-manual: Added a variable glossary description for the
SSTATE_SCAN_FILES variable.

In addition to these changes, I sprinkled in a liberal amount
of cross-referencing for the readers pleasure.

(From yocto-docs rev: 3a8ca96861f4c5d3badb91d0cdc5a3df513d4e59)

Signed-off-by: Scott Rifenbark <srifenbark@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/ref-manual/closer-look.xml

@@ -867,6 +867,19 @@
             <para>
                 This step in the build process consists of three tasks:
                 <itemizedlist>
+                    <listitem><para>
+                        <emphasis><link linkend='ref-tasks-prepare_recipe_sysroot'><filename>do_prepare_recipe_sysroot</filename></link>:</emphasis>
+                        This task sets up the two sysroots in
+                        <filename>${</filename><link linkend='var-WORKDIR'><filename>WORKDIR</filename></link><filename>}</filename>
+                        (i.e. <filename>recipe-sysroot</filename> and
+                        <filename>recipe-sysroot-native</filename>) so that
+                        the sysroots contain the contents of the
+                        <link linkend='ref-tasks-populate_sysroot'><filename>do_populate_sysroot</filename></link>
+                        tasks of the recipes on which the recipe
+                        containing the tasks depends.
+                        A sysroot exists for both the target and for the native
+                        binaries, which run on the host system.
+                        </para></listitem>
                     <listitem><para><emphasis><filename>do_configure</filename>:</emphasis>
                         This task configures the source by enabling and
                         disabling any build-time and configuration options for