minibar: better implementation of word replacement

Instead of trying to reconstruct the abstract tree from the bracketed string,
use the node numbers (the field called "fid") to identify which node in the
abstact syntax tree a word in the bracketed string corresponds to.

src/www/minibar/minibar_translations.js

@@ -178,6 +178,7 @@ Translations.prototype.parsetree_button=function(abs,lang) {
 function draw_brackets(b) {
     return b.token
 	? span_class("token",text(b.token))
-	: node("span",{"class":"brackets",title:(b.fun||"_")+":"+b.cat},
+	: node("span",{"class":"brackets",
+		       title:(b.fun||"_")+":"+b.cat+" "+b.fid+":"+b.index},
 	       b.children.map(draw_brackets))
 }