Add cancel button to advanced scenario details (re #685)

rsrc/dialogs/edit-scenario-advanced.xml

@@ -1,7 +1,7 @@
 <?xml version='1.0' encoding='UTF-8' standalone='no'?>
 <!-- NOTE: This file should be updated to use relative positioning the next time it changes. -->
 <?xml-stylesheet href="dialog.xsl" type="text/xsl"?>
-<dialog defbtn='okay'>
+<dialog defbtn='okay' escbtn='cancel'>
 	<pict type='dlog' num='16' top='8' left='8'/>
 	<text size='large' top='6' left='50' width='256' height='17'>Scenario Advanced Details</text>
 
@@ -32,4 +32,5 @@
 	<button name='bg-fight' type='tiny' top='235' left='180'>In combat:</button>
 
 	<button name='okay' type='regular' top='304' left='395'>OK</button>
+	<button name='cancel' type='regular' relative='neg pos-in' rel-anchor='prev' top='0' left='73'>Cancel</button>
 </dialog>