X11 getlin()'s prompt

Reissuing getlin() with a different prompt wasn't reliably resizing the
X11 prompt widget.  After a lot of hacking away at win/X11/dialogs.c I
eventually tried setting the response portion of the widget first and
got much better results, enough to throw away the tentative changes to
dialogs.c.

There's still a lot of room from improvement but I think it would need
to replace the ghostview prompting instead of trying to massage that.

doc/fixes3-7-0.txt

@@ -1665,6 +1665,8 @@ X11: with 'slow' resource set to False, the pop up yn_function didn't always
 X11: (possibly X11+OSX): if persistent inventory was displayed at time of
 	end-of-game prompting, prompting would stall until that window was
 	manually dismissed
+X11: (possibly X11+OSX): try harder to resize the getlin() prompt, if needed,
+	when prompt text changes
 X11: set all selectable menu lines to the same length, left justified
 X11: initializing the get-extended-command widget modified memory beyond what
 	it dynamically allocated