Fix installation group ownership of theme files (ticket 2345).

themes/Makefile.am

@@ -11,8 +11,7 @@ install-data-local:
 	for tf in $(THEME_FILES); do \
 		gzip -d -c < $(srcdir)/$$tf | (cd $(THEME_DIR); tar -xmf -); \
 	done
-	-if [ -n "$(USER)" ]; then chown -R $(USER) $(THEME_DIR); else chown -R root $(THEME_DIR); fi
-	
+	-if [ "$$EUID" = "0" ]; then chown -R 0:0 $(THEME_DIR); fi
 
 uninstall-local:
 	-for tf in $(THEME_FILES); do \