org-list: Fix bug when repairing checkbox with an ORDERED property

* lisp/org-list.el (org-list-struct-fix-box): When a checkbox has to
  be resetted because of a non-nil ORDERED property value, make sure
  it had a checkbox already.
Merge branch 'maint'
org-element: Change return value for element at point in some corner cases

* lisp/org-element.el (org-element-at-point): When point is before any
  element, in the first blank lines of the buffer, return nil.  When
  point is within blank lines just after a headline, return that
  headline.
(org-element-context): Return nil when point is within the blank at
the beginning of the buffer.
* testing/lisp/test-org-element.el: Add tests.
Rewrite C-c C-c using Elements

* lisp/org.el (org-ctrl-c-ctrl-c): Rewrite function using Elements.
org-element: Improve some docstrings

* lisp/org-element.el (org-element-parse-buffer, org-element-map,
  org-element-at-point, org-element-context): Be more verbose in
  docstrings.  Also fix typos.
Merge branch 'maint'

Conflicts:
	lisp/org-element.el
Allow C-c C-c to act on item anywhere on its first line

* lisp/org.el (org-ctrl-c-ctrl-c): Anywhere on the first line of an
  item, act on that item, provided no other object is found under the
  point.  Fix bug when function is called on a footnote definition
  attribute.

This is a convenience feature mimicing old behaviour, but it is an
aberration from the structure POV.