[gimp-help-2] Add docs for all new layer lock buttons, update screenshots

[Alexandre Prokoudine <aprokoudine src gnome org>]

commit 1fe16728c1a1d1d1c44e0833e3c864e3ef145f93
Author: Alexandre Prokoudine <alexandre prokoudine gmail com>
Date:   Mon Jan 30 03:22:26 2017 +0300

    Add docs for all new layer lock buttons, update screenshots

 images/C/dialogs/lock-alpha.png         |  Bin 5683 -> 9699 bytes
 images/C/dialogs/lock-pixels.png        |  Bin 0 -> 9832 bytes
 images/C/dialogs/lock-position-size.png |  Bin 0 -> 9810 bytes
 src/concepts/layers.xml                 |   55 +++++++++++++++++++++++++++----
 4 files changed, 48 insertions(+), 7 deletions(-)
---
diff --git a/images/C/dialogs/lock-alpha.png b/images/C/dialogs/lock-alpha.png
index c35ac10..b302f26 100644
Binary files a/images/C/dialogs/lock-alpha.png and b/images/C/dialogs/lock-alpha.png differ
diff --git a/images/C/dialogs/lock-pixels.png b/images/C/dialogs/lock-pixels.png
new file mode 100644
index 0000000..14b494e
Binary files /dev/null and b/images/C/dialogs/lock-pixels.png differ
diff --git a/images/C/dialogs/lock-position-size.png b/images/C/dialogs/lock-position-size.png
new file mode 100644
index 0000000..c105c36
Binary files /dev/null and b/images/C/dialogs/lock-position-size.png differ
diff --git a/src/concepts/layers.xml b/src/concepts/layers.xml
index afc3b0d..aa24ac2 100644
--- a/src/concepts/layers.xml
+++ b/src/concepts/layers.xml
@@ -425,16 +425,57 @@
       </varlistentry>
 
       <varlistentry>
+        <term><quote>Lock pixels</quote> setting</term>
+        <listitem>
+          <para>
+            This toggle button enables and disables protection from painting 
+            over the currently selected layer. When the button is pressed 
+            down, you cannot use any brush-based tool (Paintbrush, Pencil, 
+            Eraser etc.), the Airbrush or the Ink tool on the currently 
+            selected layer.
+          </para>
+          <figure>
+            <title>Lock pixels</title>
+            <mediaobject>
+              <imageobject>
+                <imagedata format="PNG"
+                  fileref="images/dialogs/lock-pixels.png"/>
+              </imageobject>
+            </mediaobject>
+          </figure>
+        </listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><quote>Lock position and size</quote> setting</term>
+        <listitem>
+          <para>
+            This toggle button enables and disables protection of layers from 
+            moving them around or transforming them. When the button is 
+            pressed down, you cannot use any transform tool (Rotate, Shear, 
+            Perspective and others) or move it.
+          </para>
+          <figure>
+            <title>Lock position and size</title>
+            <mediaobject>
+              <imageobject>
+                <imagedata format="PNG"
+                  fileref="images/dialogs/lock-position-size.png"/>
+              </imageobject>
+            </mediaobject>
+          </figure>
+        </listitem>
+      </varlistentry>
+
+      <varlistentry>
         <term><quote>Lock alpha channel</quote> setting</term>
         <listitem>
           <para>
-            In the upper left corner of the Layers dialog appears a small
-            checkbox that controls the <quote>Lock</quote>
-            setting for the transparency of the layer (see the figure below).
-            If this is checked, then the alpha channel for the layer is
-            locked, and no manipulation has any effect on it. In particular,
-            nothing that you do to a transparent part of the layer will have
-            any effect.
+            This toggle button controls the <quote>Lock</quote> setting for 
+            the transparency of the layer (see the figure below). If this is 
+            checked, then the alpha channel for the layer is locked, and no 
+            manipulation has any effect on it. In particular, nothing that 
+            you do to a transparent part of the layer will have any effect.
           </para>
           <figure>
             <title>Lock Alpha channel</title>