This benefits script authors and testers of ScriptFu.
Now a call to (display "foo") in a plugin goes to the terminal where GIMP started.
Whether interactive or in batch mode.
Make TS errors go to an error port instead of the output port.
Tool plugins: Console, Eval, Server get error messages from the error port.
TextConsole not changed. Tools behave per new doc "ScriptFu Tools" at dev web site.
Driveby fix of SF Server: send whole message instead of byte by byte.
Driveby comments and more semantic checking of set-output-port in TS.
Add test plugin test-display.scm
