org-element: Return nil for unspecified time values

* lisp/org-element.el (org-element-timestamp-parser): Return nil for
  unspecified :hour-end and :minute-end properties.
* testing/lisp/test-org-element.el: Add tests.
Change fontification order for links

* lisp/org.el (org-set-font-lock-defaults): let footnote fontifications
  be done before other links' fontification. This allows links appearing
  inside footnotes to be both visible and active.

TINYCHANGE
org-export: New `org-export-derived-backend-p' predicate

* contrib/lisp/org-export.el (org-export-define-derived-backend): Add
  `:parent' property to derived backend.
(org-export-derived-backend-p): New function.
* testing/lisp/test-org-export.el: Add tests.

This function can be useful in filters implemation. I.e.

  (defun my-filter (contents backend info)
    (when (memq backend '(e-latex e-beamer some-derived-backend-from-latex))
      ...))

can be replaced with:

  (defun my filter (contents backend info)
    (when (org-export-derived-backend-p backend 'e-latex)
      ...))
org-e-latex: Stuff label and caption within special blocks

* contrib/lisp/org-e-latex.el (org-e-latex-special-block): Stuff label
  and caption within special blocks.
Allow more flexible customization of clocksum format

* lisp/org.el (org-time-clocksum-format, org-time-clocksum-fractional-format):
in addition to a single format string, the clocksum formats can now be
plists specifying separate formats for different time units.

* lisp/org.el (org-minutes-to-clocksum-string): new function to
replace org-minutes-to-hh:mm-string, which converts a number of
minutes to a string according to the customization options.

* lisp/org-colview.el (org-columns-number-to-string): use new
org-minutes-to-clocksum-string function to format clocksum durations.

* lisp/org-clock.el: always call new org-minutes-to-clocksum-string
function when formatting time durations, instead of calling
org-minutes-to-hh:mm-string or passing org-time-clocksum-format
directly to format.
Silence byte compiler

* contrib/lisp/org-invoice.el (org-invoice-info-to-table,
  org-invoice-list-to-table): Silence byte compiler.
* lisp/org-agenda.el (org-agenda-show-clocking-issues,
  org-agenda-format-item): Silence byte compiler.
* lisp/org-colview-xemacs.el (org-agenda-columns): Silence byte
  compiler.
* lisp/org-colview.el (org-agenda-columns): Silence byte compiler.
* lisp/org.el (org-properties-postprocess-alist): Silence byte
  compiler.

Function renaming was necessary as of
a00a7b29183798c36ab75698a4ef5c3db4e670ec.
org-e-latex: Fixes bug introduced by commit 907110e

* contrib/lisp/org-e-latex.el: Floating tables get a \centering
  declaration, otherwise the table get wrapped in \begin{center}
  and \end{center} environment.

Thanks to Andreas Leha for reporting it.

TINYCHANGE
"none" header avoids result post-process

This patch introduces a new header argument which hide all code block
results from Emacs so that they are not processed into Emacs-lisp
objects; a process which may take a great deal of time for large
objects.

* lisp/ob.el (org-babel-common-header-args-w-values): Adding the new
  "none" header argument.
  (org-babel-execute-src-block): Don't do *any* result processing if the
  "none" header argument has been specified.
  (org-babel-sha1-hash): Remove the none header argument from
  header arg lists when calculating cache sums.
  (org-babel-insert-result): Flesh out some documentation.
org-e-beamer: Fix "columns" environment when explicitly requested

* contrib/lisp/org-e-beamer.el (org-e-beamer-environments-special):
  Add "columns" as a new special environment.
(org-e-beamer--format-block): Allow options in columns environment
when explictly requested as a BEAMER_env property.  Small refactoring.
org-e-beamer: Add "fullframe" special environment

* contrib/lisp/org-e-beamer.el (org-e-beamer-environments-special):
  Add "fullframe" environment.  Change access key for "againframe".
(org-e-beamer--frame-level): "fullframe" environment also sets the
frame level for the tree.
(org-e-beamer--format-frame): Ignore headline title when environment
is "fullframe".
(org-e-beamer-select-environment): Change access key for "againframe".
still execute code block even if :results none

* lisp/ob.el (org-babel-execute-src-block): Fixed bug introduced in
  d4b739f.