bug#28937: 26.0.60; Value after elisp docstring is filled (boundaries on forward-paragraph)

[Alex]

Consider:

(defun test ()
  "This is a test docstring.
Here is some more text."
  1
  2
  3
  4
  5)
  
In an Emacs Lisp/Lisp Interaction buffer press `M-q' anywhere in the
docstring to fill the above. Notice that 1 through 5 are all filled with
the docstring, when none of them should be. Now consider:

(defun test ()
  "This is a test docstring.
Here is some more text."
  1
  2
  (3)
  4
  5)

Now only 1 and 2 are filled. This is because forward-paragraph uses the
`paragraph-start' regexp to find the start of a new paragraph. This
regexp includes `(', which is why everything from (3) isn't filled.

What should likely be done is to find the end of the docstring when
filling it and stopping the search if it reaches the end.

forward-paragraph should accept an arbitrary point as a search limit to
accomplish the above.

Once this bug is fixed, the space+colon added in bug#24622 should be
removed.