ref-manual, dev-manual, bsp-guide: Applied Paul Eggleton Build history patch 4 of 5.

* BBFILES should be appended to with +=

* BBPATH should be appended to with .=

* Immediate expansion is not necessary for BBFILE_PRIORITY

* Immediate expansion is not necessary for references in layer.conf
  to LAYERDIR since these are automatically expanded at the end of
  parsing the file (and have been for some time).

* Add collection name override to BBFILE_PRIORITY example

* Fix comments referring to old structure ("packages directory" or
  "recipes directory")

(From yocto-docs rev: 0aaac8f5ad97c802ebe1d4f3ffb7987050533292)

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

documentation/ref-manual/ref-variables.xml

@@ -1869,10 +1869,8 @@ recipes-graphics/xorg-font/font-alias_1.0.3.bb:PR = "${INC_PR}.3"
             <glossdef>
                 <para>When used inside the <filename>layer.conf</filename> configuration
                     file, this variable provides the path of the current layer.
-                    This variable requires immediate expansion
-                    (see the BitBake manual) as lazy expansion can result in
-                    the expansion happening in the wrong directory and therefore
-                    giving the wrong value.</para>
+                    This variable is not available outside of <filename>layer.conf</filename>
+                    and references are expanded immediately when parsing of the file completes.</para>
             </glossdef>
         </glossentry>