reporting deleted lines when at blank lines

when backspacing at the beginning of a line, if the previous line is
blank, then report that line as being deleted instead of the current
line; reset the modified line always (it will be set by the movement of
the cursor when the backspace is processed), but ignore the change if
the cursor is at the end of the line (the current line is blank)

when deleting at the end of a line, if the next line is blank, then
ignore the change since the previous line does not actually get modified

also added break statements to the delete and backspace if statements to
break out of the default case in the switch statement so that no further
checks are made