Clarify undo/redo tooltips (fixes #1670)

data/core.yaml

@@ -129,8 +129,12 @@ en:
         multiple: "Split {n} lines/area boundaries."
       not_eligible: Lines can't be split at their beginning or end.
       multiple_ways: There are too many lines here to split.
-  nothing_to_undo: Nothing to undo.
-  nothing_to_redo: Nothing to redo.
+  undo:
+    tooltip: "Undo: {action}"
+    nothing: Nothing to undo.
+  redo:
+    tooltip: "Redo: {action}"
+    nothing: Nothing to redo.
   tooltip_keyhint: "Shortcut:"
   just_edited: "You just edited OpenStreetMap!"
   browser_notice: "This editor is supported in Firefox, Chrome, Safari, Opera, and Internet Explorer 9 and above. Please upgrade your browser or use Potlatch 2 to edit the map."

dist/locales/en.json

@@ -166,8 +166,14 @@
             "multiple_ways": "There are too many lines here to split."
         }
     },
-    "nothing_to_undo": "Nothing to undo.",
-    "nothing_to_redo": "Nothing to redo.",
+    "undo": {
+        "tooltip": "Undo: {action}",
+        "nothing": "Nothing to undo."
+    },
+    "redo": {
+        "tooltip": "Redo: {action}",
+        "nothing": "Nothing to redo."
+    },
     "tooltip_keyhint": "Shortcut:",
     "just_edited": "You just edited OpenStreetMap!",
     "browser_notice": "This editor is supported in Firefox, Chrome, Safari, Opera, and Internet Explorer 9 and above. Please upgrade your browser or use Potlatch 2 to edit the map.",

js/id/ui/undo_redo.js

@@ -20,7 +20,9 @@ iD.ui.UndoRedo = function(context) {
             .placement('bottom')
             .html(true)
             .title(function (d) {
-                return iD.ui.tooltipHtml(d.annotation() || t('nothing_to_' + d.id), d.cmd);
+                return iD.ui.tooltipHtml(d.annotation() ?
+                    t(d.id + '.tooltip', {action: d.annotation()}) :
+                    t(d.id + '.nothing'), d.cmd);
             });
 
         var buttons = selection.selectAll('button')