mk/default.mk, testing/org-test.el: set org-startup-folded to nil

* mk/default.mk (BATCH), testing/org-test.el: Set `org-startup-folded´
  to nil to avoid lots of "OVERVIEW" messages cluttering the output.
Documentation for :export: tag usage

* doc/org.texi (Export settings): documentation describing how text
above the first heading is ignored when an :export: tag is in a file.

Commit 7cf4406088d4d7f50c35c6ba7ca3c351db2086bc introduced a feature of
the exporter that ignores text above the first headline when an :export:
tag is used anywhere in a file. This commit documents that behaviour
introduced in 7cf44060, in doc/org.texi.

TINYCHANGE
Merge branch 'maint'
support for D language code blocks in contrib

  Thanks for Thierry Banel for contributing ob-D.
org-element: Implement `org-element-secondary-p'

* lisp/org-element.el (org-element-secondary-p): New function.
* lisp/ox.el (org-export-get-previous-element,
  org-export-get-next-element): Use new function.
* testing/lisp/test-org-element.el (test-org-element/secondary-p): New
  test.
org-element: Implement `org-element-extract-element'

* lisp/org-element.el (org-element-extract-element): New function.
* testing/lisp/test-org-element.el (test-org-element/extract-element):
  New test.
org-element: Implement `org-element-insert-before'

* lisp/org-element.el (org-element-insert-before): New function.
* testing/lisp/test-org-element.el (test-org-element/insert-before):
  New test.
org-element: Extend `org-element-set-element' to strings

* lisp/org-element.el (org-element-set-element): Allow to replace
  a string with an element, an element with a string, or a string with
  a string.
ox-bibtex: Small refactoring

* contrib/lisp/ox-bibtex.el (org-bibtex-process-bib-files): Execute
  function only when back-end is HTML.
ox-bibtex: Merge consecutive citations

* contrib/lisp/ox-bibtex.el (org-bibtex-merge-contiguous-citations):
  New function.
(org-latex-link, org-html-link): Remove advices.
add  --set=\"ON_ERROR_STOP=1\" to psql execution

  Thanks to Joost Helberg for suggesting this change.

* lisp/ob-sql.el (org-babel-execute:sql): Add
  --set=\"ON_ERROR_STOP=1\" to psql execution.
ascii export backend support to ox-bibtex w/pandoc
Fix customization types in org-drill.el

* contrib/lisp/org-drill.el (org-drill-leech-method):
(org-drill-scope):
(org-drill-spaced-repetition-algorithm): Fix customization types.
Fix customization types in org-drill.el

* contrib/lisp/org-drill.el (org-drill-leech-method):
(org-drill-scope):
(org-drill-spaced-repetition-algorithm): Fix customization types.
ox-bibtex: Tiny refactoring

* contrib/lisp/ox-bibtex.el (org-bibtex-process-bib-files): Tiny
  refactoring.
ox-html: Fix LaTeX fragments export

* lisp/ox-html.el (org-html-format-latex): Add an argument.  Ensure
  latex header is the same as specified in the original buffer when
  exporting a LaTeX fragment or environment.
(org-html-latex-environment, org-html-latex-fragment): Apply signature
change.
Merge branch 'maint'

Conflicts:
	contrib/lisp/org-drill.el
ox-publish: Introduce `org-publish-after-publishing-hook'

* lisp/ox-publish.el (org-publish-after-publishing-hook): New variable.
(org-publish-file): Call hook with file name and output file name as
arguments.  Small refactoring.
(org-publish-attachment): Return output file.
Fix C-c C-c behaviour on some objects

* lisp/org.el (org-ctrl-c-ctrl-c): When point is on an unsupported
  object, look for something to do at a higher level instead of
  bailing out.

For example, C-c C-c should toggle checkbox in the following example
even though X point is technically on a subscript.

  - [ ] a_Xb
Merge branch 'maint'