Record Activity task broken with large numbers of contacts since 4.5

Since the introduction of Select2 - I think - the Record Activity search task has used Select2 for the "With" field. This renders the form useless when you need to do a large bulk addition of activities because it crashes the user's browser trying to generate that many entries in the Select2 widget!

This means the only way to record an activity for large numbers of contacts is now by exporting the list and creating a spreadsheet for the Activities Import. This makes a 2 minute job into a tricky much longer job that requires more technical knowledge and has more scope to go wrong.

I believe that the old behaviour was to list contacts as a read-only field. I do not think it is sensible to have a user-editable field with thousands of contacts. Nobody is going to edit that field. Having it as editable is good for the up-to-a-handful of contacts case only.

Also, IMO, it should not be possible to crash your browser by operating CiviCRM.