Fix #713: support <label> for <input type=file> (#715)

Author: rr-

common/content/buffer.js

@@ -530,6 +530,9 @@ const Buffer = Module("buffer", {
             Buffer.openUploadPrompt(elem);
             buffer.lastInputField = elem;
         }
+        else if (elem instanceof HTMLLabelElement && elem.control) {
+            Buffer.focusElement(elem.control);
+        }
         else {
             elem.focus();
 
@@ -637,6 +640,10 @@ const Buffer = Module("buffer", {
             Buffer.openUploadPrompt(elem);
             return;
         }
+        else if (elem instanceof HTMLLabelElement && elem.control) {
+            buffer.followLink(elem.control, where);
+            return;
+        }
 
         let ctrlKey = false, shiftKey = false;
         switch (where) {