[PATCH v2] ref-manual: update glossary entries for packaging backend variables

Either clarify or correct the packaging backend information for the
package exclusion variables:

  -  PACKAGE_EXCLUDE
  -  BAD_RECOMMENDATIONS
  -  NO_RECOMMENDATIONS

Signed-off-by: Robert P. J. Day <[email protected]>

---

diff --git a/documentation/ref-manual/variables.rst b/documentation/ref-manual/variables.rst
index df3666f1c..82ff48fd5 100644
--- a/documentation/ref-manual/variables.rst
+++ b/documentation/ref-manual/variables.rst
@@ -300,6 +300,9 @@ system and gives an overview of their function and contents.
       variable), the OpenEmbedded build system ignores your request and
       will install the packages to avoid dependency errors.

+      This variable is supported for the RPM and IPK packaging backends,
+      but not for DEB.
+
       See the :term:`NO_RECOMMENDATIONS` and the
       :term:`PACKAGE_EXCLUDE` variables for related
       information.
@@ -6498,8 +6501,7 @@ system and gives an overview of their function and contents.
          functionality, such as kernel modules. It is up to you to add
          packages with the :term:`IMAGE_INSTALL` variable.

-      This variable is only supported when using the IPK and RPM
-      packaging backends. DEB is not supported.
+      This variable is supported for all packaging backends.

       See the :term:`BAD_RECOMMENDATIONS` and
       the :term:`PACKAGE_EXCLUDE` variables for
@@ -6930,8 +6932,7 @@ system and gives an overview of their function and contents.
       an iterative development process to remove specific components from a
       system.

-      This variable is supported by all of the RPM, DEB and IPK
-      packaging backends.
+      This variable is supported for all packaging backends.

       See the :term:`NO_RECOMMENDATIONS` and the
       :term:`BAD_RECOMMENDATIONS` variables for