[TxMt] block undo/redo

[Andreas Wahlin]

Please please Allan include block undo/redo. At least as an option.  
Not only is it standard on all other programs (that I know of) I find  
it far more usable. If I want the latest character I typed undone,  
I'll hit backspace.
I currently sit and try to figure out a good XML scheme for myself,  
and I find that I change whole words very much, such as tag-names and  
allowed values for attributes, it's a pain to hit the undo button so  
many times as is necessary.

Andreas