Use Delete key to merge two consecutive lists

Consider the following input:

* item A1
* item A2

* item B1
* item B2

Pressing Delete after "item A2" should merge the two lists:

* item A1
* item A2
* item B1
* item B2

The current behavior is:

* item A1
* item A2item B1

* item B2

Note that the default editor ( http://www.mozilla.org/editor/midasdemo/ ) has the right behavior, but we have overwritten it.

When the two consecutive lists are of different types the default editor merges the lists by changing the type of the second one:

* item1

1. item2

becomes

* item1
* item2

I think we can adopt this behavior too.