Restore Error workaround in Bluebird to produce proper line numbers

I didn't really investigate this, but errors from the outside world seem
to not pass the "obj instanceof Error" test due to some weirdness that
Bluebird is doing. (When I took this out recently I thought we just were
throwing some custom errors that didn't properly extend Error, but that
isn't the issue.) This restores the earlier workaround.

resource/bluebird.js

@@ -4675,6 +4675,9 @@ function originatesFromRejection(e) {
 }
 
 function canAttachTrace(obj) {
+    // Added by Zotero
+    return obj.message && obj.stack && es5.propertyIsWritable(obj, "stack");
+    
     return obj instanceof Error && es5.propertyIsWritable(obj, "stack");
 }