org-export: Limit depth of headline collection to headline level

* contrib/lisp/org-export.el (org-export-collect-headlines): By
  default, limit depth of headline collection to last headline level.
* contrib/lisp/org-e-html.el (org-e-html-toc): Small refactoring.
org-export: Nil value from a filter means filter will be skipped

* contrib/lisp/org-export.el (org-export-filter-apply-functions): Nil
  value from a filter means filter will be skipped. To ignore the
  current element or object, the filter has to return the empty string
  instead.

This change is done to ease filter writing. When writing
a backend-specific filter (and I guess most are), there's no more need
for the somewhat contrived:

  (if (not (eq backend 'e-latex)) data
    ... filter's job...)

A more straightforward:

  (when (eq backend 'e-latex)
    ... filter's job...)

is now enough.

On the other hand, it is not possible anymore to specify 'ignore as
a filter to ignore every element or object of a given type. To
achieve that goal, one can now write, for example:

  (add-to-list 'org-export-filter-example-block-functions
                 (lambda (value backend info)
                   (when (eq backend 'e-html) "")))

It will ignore every example block in the `e-html' export back-end.
org-export: Run export hook with current back-end as argument

* contrib/lisp/org-export.el (org-export-as): Run export hook with
  current back-end as argument.
* testing/lisp/test-org-export.el: Update test.
org-export: Make sure back-end specific filters do not make any back-end check

* contrib/lisp/org-e-ascii.el (org-e-ascii-filter-headline-blank-lines):
  Remove backend check.
* contrib/lisp/org-e-texinfo.el (org-e-texinfo-filter-section-blank-lines):
  Remove backend check.
* contrib/lisp/org-export.el (org-export-define-backend): Update
  docstring accordingly.
org-export: Small clean-up
org-e-texinfo.el: Tiny formatting and code fix

* org-e-texinfo.el (org-e-texinfo-table-column-widths): Remove
a quote before a lambda expression.
Implement key replacement depending on the contexts.

* org.el (org-contextualize-agenda-or-capture): Handle key
replacement depending on the contexts.

* org-capture.el (org-capture-templates-contexts): Allow to
use the context as a way to replace one capture template by
another one.

* org-agenda.el (org-agenda-custom-commands-contexts): Allow
to use the context as a way to replace one agenda custom
command by another one.

* org.texi (Templates in contexts): Document the new structure
of the variables `org-agenda-custom-commands-contexts' and
`org-capture-templates-contexts'.

In the setup below, X is not a real capture template, it is just
an alias to templates A and B in .txt and .el files.  A and B are
deactivated by default in all files.

(setq org-capture-templates
      '(("X" "Nothing but an alias")
	("A" "AAAA" entry (file+headline [...]))
	("B" "BBBB" entry (file+headline [...]))))

(setq org-capture-templates-contexts
      '(("A" "A" ((not-in-file . ".*")))
	("B" "B" ((not-in-file . ".*")))
	("X" "A" ((in-file . "\\.txt")))
	("X" "B" ((in-file . "\\.el")))))

Thanks to Carsten for suggesting this "key-replacement" idea!
org.el (org-contextualize-agenda-or-capture): Normalize contexts

* org.el (org-contextualize-agenda-or-capture): Normalize
contexts.
Update the handling of agenda/capture keys contextualization.

* org.el (org-contextualize-keys): Rename from
`org-contextualize-agenda-or-capture'.  Fix normalization to
handle empty key replacement string.
(org-contextualize-validate-key): Rename from
`org-contexts-validate'.  Allow checking against a custom
function.

* org-agenda.el (org-agenda-custom-commands-contexts): Update.
(org-agenda): Use `org-contextualize-keys'.

* org-capture.el (org-capture-templates-contexts): Ditto.

* org.texi (Templates in contexts, Setting Options): Update to
reflect changes in how contexts options are processed.
org-element: Paragraphs don't end at incomplete latex environments

* lisp/org-element.el (org-element-paragraph-separate): Since this
  variable is meant to be searched forward, \end{...} shouldn't
  trigger the end of a paragraph before checking if it is the end of
  a complete environment.
(org-element-latex-environment-parser): Slight change to the regexp
matching the beginning of a latex environment.
(org-element-paragraph-parser): Paragraphs don't end at incomplete
latex environments.
(org-element-latex-or-entity-successor): Remove paragraph environments
from latex fragment search.
Auto-filling must not break current paragraph

* lisp/org.el (org-fill-paragraph-separate-nobreak-p): New function.
(org-set-autofill-regexps): Introduce new predicate.
(org-fill-item-nobreak-p): Remove function.
Do not fill verse blocks contents

* lisp/org.el (org-fill-context-prefix, org-fill-paragraph): Do not
  fill verse blocks contents.  Verse blocks can be used to format
  free-form poetry, so filling has to be done manually.
* testing/lisp/test-org.el: Remove unnecessary tests.
org.el: Fix the contextual check against a function

* org.el (org-contextualize-validate-key): Fix the check
against a function.
Merge branch 'master' of orgmode.org:org-mode
Fix comment auto-filling

* lisp/org.el (org-set-autofill-regexps): Install new comment line
  break function.
(org-comment-line-break-function): New function.
(org-mode): Remove unnecessary line.
org-capture.el: Protect the text used for replacement from being further replaced

* org-capture.el (org-capture-fill-template): Protect the text
used for replacement from being further replaced.

Thanks to Moritz Ulrich for reporting this bug.
org-agenda.el: Fix bug about restoring existing window conf

* org-agenda.el (org-prepare-agenda-window): Use
`org-pre-agenda-window-conf' if already set.
(org-agenda-Quit): Set `org-pre-agenda-window-conf' to nil
when quitting.
(org-agenda-quit): Ditto.

Thanks to Moritz Ulrich for reporting a bug about this.
utils/server.mk: include utils/org-fixup.el and utils/org-install.el in release target
utils/server.mk: include utils/org-fixup.el and utils/org-install.el in release target
Merge branch 'maint'