org.el (org-mode): Don't initialize `org-beamer-mode' when `org-inhibit-startup' is non-nil

* org.el (org-mode): Don't initialize `org-beamer-mode' when
`org-inhibit-startup' is non-nil.
org.el (org-agenda-inhibit-startup): Rename from `org-agenda-inhibit-startup-visibility-cycling'

* org.el (org-agenda-inhibit-startup): Rename from
`org-agenda-inhibit-startup-visibility-cycling'.
(org-agenda-prepare-buffers): Bind `org-inhibit-startup' to
`org-agenda-inhibit-startup'.
Merge branch 'maint'

Conflicts:
	lisp/org.el
org-export: Fix subtree export when parent section is empty

* contrib/lisp/org-export.el (org-export--get-subtree-options): When
  point is at an headline and subtree export is called, make sure
  export properties are extracted from parent headline.
* testing/lisp/test-org-export.el: Add test.
fix bug: tangling #+headers: lines w/prefix arg