release-chore: Preparations for 0.26.0. Backfill of ReleaseNotes.

Bumping version to 0.26.0. Adding stub news entries related to the
release into news.texi and ReleaseNotes.gsdoc.

Also, this commit backfills ReleaseNotes for releases 0.24.1, 0.25.0
and 0.25.1.

Documentation/ReleaseNotes.gsdoc

@@ -16,10 +16,85 @@
       <heading>Gui Release Notes</heading>
       <p>
         The release notes include descriptions of API changes, behavior
-	changes and other information that might help developers and users
-	migrate to using a newer version of the library.
+        changes and other information that might help developers and users
+        migrate to using a newer version of the library.
       </p>
 
+      <section>
+        <heading>0.26.0</heading>
+        <p>
+          Bumped due to binary incompatibilities between 0.25.0 and 0.25.1. Also
+          including numerous compatibility improvements from the Summer of Code
+          project.
+        </p>
+        <deflist>
+          <term>TODO</term>
+          <desc>This list is yet to be written.</desc>
+        </deflist>
+      </section>
+
+      <section>
+        <heading>0.25.1</heading>
+        <p>
+          New release.
+        </p>
+        <deflist>
+          <term>Image library fixes.</term>
+          <desc>
+            JPEG (saving) alpha channel fixes and size with resolution != 72.
+            JPEG resolution read support.
+            TIFF saving fixes.
+          </desc>
+          <term>Mounting.</term>
+          <desc>Improved volumes mounting and support. Portability improvements
+          in volume mounting and support</desc>
+          <term>Text layout.</term>
+          <desc>Corrected layout of empty strings.</desc>
+          <term>Optimizations.</term>
+          <desc>Only update visible menus.</desc>
+        </deflist>
+      </section>
+
+      <section>
+        <heading>0.25.0</heading>
+        <p>
+          New release. Bumped due to detected binary incompatibility between
+          0.24.0 and 0.24.1.
+        </p>
+        <deflist>
+          <term>GIF library update</term>
+          <desc>Fixes for new GIF library versions</desc>
+          <term>Theming improvements</term>
+          <desc>Theming of named images for specific applications by the use of
+          the CFBundleIdentifier in the theme. New icons and corresponding
+          constants for special folders, recycler and others.</desc>
+          <term>NSWorkspace</term>
+          <desc>Improvements in NSWorkspace icon lookup. Improvements in
+          removable media commands, imported and cleaned from GWorkspace.</desc>
+          <term>Other</term>
+          <desc>Numerous bug fixes and improvements in Cocoa compatibility.
+          Spanish locale.</desc>
+      </section>
+
+      <section>
+        <heading>0.24.1</heading>
+        <p>
+          From a look through ChangeLog, we can see a lot of bugfixes for this
+          release, with the main focus on avoiding display glitches and
+          improving OSX compatibility.
+        </p>
+        <deflist>
+          <term>NSColorListChangedNotification</term>
+          <desc>Removed.</desc>
+          <term>NSColorPanelColorChangedNotification</term>
+          <desc>Removed.</desc>
+          <term>NSImageInterpolation{Default,High,Low,None}</term>
+          <desc>Removed.</desc>
+          <term>NSPrintHorizonalPagination</term>
+          <desc>Removed.</desc>
+        </deflist>
+      </section>
+
      <section>
       	<heading>0.24.0</heading>
 	<p>