FIXED: if/unless one-liners after trailing backslash in ruby

Trailing backslashes were not handled, forcing if/unless one-liners break the depth counters.

```ruby
def f1
  puts 'Breaking the depth…' \
    unless true
#   ↑↑↑↑↑↑ here we ran into troubles with depth, since it was incremented
end

def f2
  # code
end
```

Fixed by introducing new `wait_for` regexp, similar to `=begin/=end`. This is probably not the most elegant way of doing this, but I didn’t want to interfere too much into your code.