ref-manual, mega-manual: Updates to the Image Generation section

Fixes [YOCTO #2808]

Applied review comments to the section from Paul Eggleton.  I
updated the figure and the text areas.

(From yocto-docs rev: a89b126861e8ee2f43a89afb0a16e56659270fee)

Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/ref-manual/closer-look.xml

@@ -907,18 +907,41 @@
                         </para></listitem>
                     <listitem><para><link linkend='var-IMAGE_FEATURES'><filename>IMAGE_FEATURES</filename></link>:
                         Specifies features to include in the image.
-                        These features map to additional packages for
+                        Most of these features map to additional packages for
                         installation.</para></listitem>
                     <listitem><para><link linkend='var-PACKAGE_CLASSES'><filename>PACKAGE_CLASSES</filename></link>:
-                        Specifies the package manager to use and consequently
+                        Specifies the package backend to use and consequently
                         helps determine where to locate packages within the
                         Package Feeds area.</para></listitem>
                     <listitem><para><link linkend='var-IMAGE_LINGUAS'><filename>IMAGE_LINGUAS</filename></link>:
-                        Determines the language for which packages are being 
-                        installed.</para></listitem>
+                        Determines the language(s) for which additional
+                        language support packages are installed.
+                        </para></listitem>
                 </itemizedlist>
             </para>
 
+            <para>
+                The process runs all of the post installation scripts, and
+                any that fail to run on the build host will be run on the
+                target when the target system is first booted.
+                If you are using a read-only root filesystem, all the post
+                installation scripts must succeed during the package
+                installation phase since the root filesystem cannot be
+                written into.
+            </para>
+
+            <para>
+                During Optimization, optimizing processes are run across
+                the image.
+                These processes include <filename>mklibs</filename> and
+                <filename>prelink</filename>.
+                The <filename>mklibs</filename> optimizes the size of the
+                libraries.
+                A <filename>prelink</filename> process optimizes the dynamic
+                linking of shared libraries to reduce start up time of the
+                executables.
+            </para>
+
             <para>
                 Part of the image generation process includes compressing the
                 root filesystem image.
@@ -926,37 +949,10 @@
                 routines designed to reduce the overall size of the image.
             </para>
 
-            <para>
-                The process runs as many post installation scripts as possible.
-                Any scripts that cannot be run are run when the system is 
-                first booted.
-                If you are using a read-only root filesystem, all the post
-                installation scripts are run during the package installation
-                phase since the root filesystem cannot be written into.
-            </para>
-
-            <para>
-                During the Prelink phase, optimization processes are run across
-                the image. 
-                These processes include <filename>mklibs</filename> and 
-                <filename>prelink</filename>.
-                The <filename>mklibs</filename> optimizes the size of the 
-                libraries.  
-                The <filename>prelink</filename> process optimizes the dynamic 
-                linking of shared libraries to reduce start up time of the 
-                executables.
-                See the 
-                <link linkend='var-IMAGE_POSTPROCESS_COMMAND'><filename>IMAGE_POSTPROCESS_COMMAND</filename></link>
-                and 
-                <link linkend='var-ROOTFS_POSTPROCESS_COMMAND'><filename>ROOTFS_POSTPROCESS_COMMAND</filename></link>
-                variables for additional information.
-            </para>
-
             <para>
                 After the root filesystem has been constructed, the image
                 generation process turns everything into an image file or
                 a set of image files.
-                we need to turn into an image file or set of image files.  
                 The formats used for the root filesystem depend on the
                 <link linkend='var-IMAGE_FSTYPES'><filename>IMAGE_FSTYPES</filename></link>
                 variable.