Truncating the path from the right now takes in account the delimiter
length, so that directories with names shorter than truncated name +
delimiter are displayed properly.
For example, if SHORTEN_DIR_LENGTH is 4 and the delimiter is "..",
"../tests/.." and "../custom/.." are not incorrectly "truncated" to
"../test../.." and "../cust../..", both of which are longer or the same
length as the original.
