Confirmed that on Linux the serial interrupt takes precedence over the timer

interrupt, so we don't need to worry about scheduler delays.  This means the
delay can be trimmed down to 25 miliseconds.  Add comment while at it.

editors/vi.c

@@ -2280,8 +2280,9 @@ static char readit(void)	// read (maybe cursor) key from stdin
 					struct pollfd pfd;
 					pfd.fd = 0;
 					pfd.events = POLLIN;
-					// Rob needed 300ms timeout on qemu
-					if (safe_poll(&pfd, 1, /*timeout:*/ 300)) {
+					// Timeout is needed to reconnect escape sequences split
+					// up by transmission over a serial console.
+					if (safe_poll(&pfd, 1, 25)) {
 						if (safe_read(0, readbuffer + n, 1) <= 0)
 							goto error;
 						n++;