Fix Issue #33 - Incorrect action for repeat last change (.)

This change fixes the behavior of the dot command when it is used to repeat an insertion which starts with a backspace.  This was first pointed out in issue #33.

I added a (commented out) unit test which should work but doesn't.  It seems that the unit testing infrastructure doesn't register the <BS> key correctly when used in insert mode in a test.  If I'm correct about that and someone would like to help me out by suggesting where that problem may lie, I'd be happy to take a look at it so that we can properly test this.

Otherwise, this fix works well and brings Vrapper's behavior closer to Vim's in a way which is, at least to me, noticeable.