This avoids adding the "output" text properties to strings that may live
past the call to 'eshell-interactive-filter'.
* lisp/eshell/esh-mode.el (eshell-interactive-output-filter): New
function...
(eshell-interactive-print): ... call it.
(eshell-interactive-filter): Update docstring.
* lisp/eshell/esh-proc.el (eshell-interactive-process-filter)
(eshell-sentinel): Call 'eshell-interactive-output-filter'.