epm-release_upgrade: say install screen only it is not installed yet

bin/epm-release_upgrade

@@ -33,7 +33,11 @@ assure_safe_run()
 			return
 		else
 			warning "It is very dangerous to upgrade to next release from a GUI (your TERM=$TERM)."
-			warning "It is recommended install 'screen' and run upgrade via screen: '# screen epm release-upgrade'"
+			if docmd epm installed screen ; then
+				warning "You have 'screen' already installed, just run upgrade via screen: '# screen epm release-upgrade'"
+			else
+				warning "It is recommended install 'screen' and run upgrade via screen: '# screen epm release-upgrade'"
+			fi
 			fatal "or run me with --force if you understand the risk."
 		fi
 	fi