* fhandler.h (fhandler_base::get_echo_handle): New virtual method.

(class fhandler_pty_master): Add echo_r and echo_w handles constituting
	read and write side of new echo pipe.
	* select.cc (peek_pipe): On pty masters, check additionally if input
	from the echo pipe is available.
	* fhandler_tty.cc (fhandler_pty_master::doecho): Drop output_mutex
	locking.  Write output to echo pipe.
	(fhandler_pty_master::process_slave_output): Check if input is available
	in echo pipe and prefer to read from it, if so.
	(fhandler_pty_slave::write): Drop output_mutex locking.
	(fhandler_pty_master::fhandler_pty_master): Initialize echo pipe
	handles to NULL.
	(fhandler_pty_master::close): Close and NULL echo pipe handles.
	(fhandler_pty_master::setup): Create echo pipe, close in case of error.

winsup/cygwin/release/1.7.36

@@ -0,0 +1,14 @@
+What's new:
+-----------
+
+
+What changed:
+-------------
+
+
+Bug Fixes
+---------
+
+- Fix potential hang in pseudo ttys when generating ECHO output while the slave
+  is flooding the pty with output.
+  Addresses: https://cygwin.com/ml/cygwin/2015-03/msg00019.html