Persistent selection backspace issues

[gotar]

1. mcedit new_empty_file
2. type in 0123456789

now two versions:

3a. F3 5*left F3 - now digits 5-9 are marked and cursors stays above 5
4a. 2*right A backspace - the new symbol appears between 6 and 7, but after removal digit 4 is marked as well(!)

or:

3b. home F3 5*right F3 - now digits 0-4 are marked and cursor stays above 5
4b. 2*left A backspace - the new symbol appears between 2 and 3, but after removal digit 5 is marked as well(!)

This means that inserting symbol extends selection, but backspace doesn't shrink it back (while delete does) respectively to direction (every time as a result selection END moves).

And now it becames more interesting:

5a. ctrl-u - 'A' gets back between 6 and 7, but 4 remains marked
6a. ctrl-u - 'A' gets away, but acting like backspace not undo - now 3 is marked as well(!)

5b. ctrl-u - 'A' gets back between 2 and 3, but 5 remains marked
6b. ctrl-u - 'A' gets away, but just like it was backspaced not deleted, i.e. marking additional digit 6(!)

So effectively by inserting a letter, removing it and undoing both the operations our selection widened by 2 characters - while first behaviour (p. 3-4) can be logically explained, there's no place for that in undo (p. 5-6): selection should shrink back to 5 characters, not further extend.

But keep backspacing in a) scenario ;)

7a. 3-9 are marked, cursor stays above 7: press backspace 4 times - we've just lost left part of selection(!) and we're back in mark mode (just press left to see it).

[angel_il]

gotar:
3a..4a and 3b..4b fixed by #2437
i think 5a..7a fixed too.

please try fix from #2437

[gotar]

Most of the glitches are fixed now, however I've encountered some:

1. mcedit new_empty_file
2. type in 0123456789
3. F3 5*left F3 - digit '4' is not marked at this point
4. backspace, ctrl-u - digit '4' is marked now
5. left, 2*del, 2*ctrl-u - digits '4' and '5' are not marked.

So it seems something is still wrong with EditUndo (the same happened in 4.7.4).

[angel_il]

see #2456