Add one more case of alternative to cleanup (Closes: #532739)

debian/changelog

@@ -7,7 +7,7 @@ dpkg (1.15.3) UNRELEASED; urgency=low
   * Unset TAR_OPTIONS when creating/extracting tar archives for source
     packages. Closes: #530860
   * Add cleanup of known invalid (master) alternatives in preinst script.
-    Closes: #530633, #531611
+    Closes: #530633, #531611, #532739
   * Let update-alternatives fix a manual alternative with a dangling symlink
     by switching it to automatic mode. Closes: #529999
 

debian/dpkg.preinst

@@ -43,9 +43,10 @@ case "$1" in
 
     upgrade)
         # Cleanup bad alternatives that would choke with new
-        # update-alternatives (see #530633, #531611)
+        # update-alternatives (see #530633, #531611, #532739)
         clean_alternative x-terminal-emulator x-terminal-emulator.1.gz
         clean_alternative x-session-manager x-session-manager.1.gz
+        clean_alternative x-window-manager x-window-manager.1.gz
 
 	case "$2" in
 	    # Upgrade from pre-conffile dpkg.cfg