Some non-controversial fixes

a test for the fix that fixes finding presentations at the very beginning of a buffer:

```
(cl-flet ((assert-it (point &optional negate)
            (let ((result (cl-first (slime-presentation-around-or-before-point point))))
              (assert (if negate (not result) result)
                      nil "Failed to pick up presentation at point %s" point))))
  (with-temp-buffer
    (slime-insert-presentation "1234567890" `(:inspected-part 42))
    (insert "     ")
    ;; in position 1 and 2 it worked, but farther away only with the fix
    (assert-it 1)
    (assert-it 2)
    (assert-it 3)
    (assert-it 4)
    (assert-it 5)
    (assert-it 10)
    (assert-it 11)
    (assert-it 12 t)))
```