Add demonhorn face to match new image in base.

COPYING.rtro

@@ -21,6 +21,7 @@ knowledge_generic: Rederived from source of base image (http://commons.wikimedia
 knowledge_messages: Rederived from source of base image (http://commons.wikimedia.org/w/index.php?title=File:Temple_Scroll.png&oldid=65512408), public domain.
 knowledge_monsters: Rederived from source of base image (http://commons.wikimedia.org/w/index.php?title=File:Dragon.svg&oldid=65944895), licensed CC-BY-SA-3.0.
 knowledge_recipes: Rederived from source of base image (http://www.nasa.gov/mission_pages/hubble/science/hst_img_20080520.html), public domain.
+demonhorn: Reference photo by FarborAnna (https://commons.wikimedia.org/wiki/File:Afrikansk_dv%C3%A4rgget_Kallh%C3%A4lls_4H-g%C3%A5rd_4.jpg)
 
 Derivatives of unknown licensing:
 capitalhold_west: Referenced from base image capitalhold_west, of unknown licensing.

ChangeLog.rtro

@@ -1,6 +1,9 @@
 ------------------------
 Changes for top of trunk
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+2023-04-06 Daniel Hawkins
+	* flesh/demon/demonhorn.rtro.111.png: Lazily clip the new base image to fit, since it already uses the XPM palette.
+
 2023-03-25 Daniel Hawkins
 	* food/drag_steak_cooked.rtro.111.png: Add missing face for item in base.
 	* spell/Burnout/burnout.rtro.11*.png: Actually correctly set up the frames this time.