Enhanced the org-e-groff.el code to use the Groff MM letter macros

* org-e-groff.el (org-e-groff-classes): Added
letter classes.
(org-e-groff-special-tags): New variable to identify special tags.
(org-e-groff--get-tagged-content): New function to retrieve
special tagged content.
(org-e-groff--mt-head): New function to create "memo" type headers.
(org-e-groff--letter-head): New function to create "letter" type headers.
(org-e-groff-template): Handle the "letter" type.
(org-e-groff-headline): handle special tags.
Merge branch 'master' of orgmode.org:org-mode

Enhanced the org-e-groff.el code to use the Groff MM letter macros

* org-e-groff.el (org-e-groff-classes): Added
letter classes.
(org-e-groff-special-tags): New variable to identify special tags.
(org-e-groff--get-tagged-content): New function to retrieve
special tagged content.
(org-e-groff--mt-head): New function to create "memo" type headers.
(org-e-groff--letter-head): New function to create "letter" type headers.
(org-e-groff-template): Handle the "letter" type.
(org-e-groff-headline): handle special tags.
Fix some warnings.
Fix many small typos.
Revert "Don't use `org-labels'"

This reverts commit ba16c3c6f50738b070769040586945436439be76.
org.el: Fix bug about filling message headers and citations

* org.el (org-fill-paragraph): Make a command.  Fix bug about
filling message headers and citations.
org.el: Fix bugs in `org-indent-line' and `org-fill-paragraph'

* org.el (org-fill-paragraph): Correctly fill paragraph in
message-mode.
(org-indent-line): Correctly indent according to mode when
`orgstruct++-mode' is on.
(orgstruct++-mode): Add `fill-prefix' to the variable temporarily
stored in `org-fb-vars'.
 org.el (org-fill-context-prefix): Fix auto-filling in `message-mode'.

* org.el (org-fill-context-prefix): Fix auto-filling in
`message-mode'.
org.el (message-in-body-p): Move declaration up to fix compiler warning

* org.el (message-in-body-p): Move declaration up to fix compiler
warning.
Don't use `org-labels'

Reworking the previous commit which attempted to remove org-labels.

* org-compat.el (org-labels): Remove.

* org-bibtex.el (org-bibtex-headline): Don't use `org-labels'.

* ob.el (org-babel-sha1-hash, org-babel-noweb-p): Ditto.
Revert "Don't use `org-labels'"

This reverts commit 9d4e1517b69e26e393f400815b77adac3d37e16c.
org-agenda.el (org-diary): Fix tiny typo

* org-agenda.el (org-diary): Fix tiny typo.
org.el: Fix bug in `org-fill-template'

* org.el (org-fill-template): Fix bug when filling template for
a key associated to the nil value.

Thanks to Ken Williams for reporting this.
org-datetree.el: New option `org-datetree-add-timestamp'

* org-datetree.el (org-datetree-add-timestamp): New option.
(org-datetree-insert-line): Use it.
org-element: Small refactoring

* lisp/org-element.el (org-element-swap-A-B): Small refactoring.
org.el: New command ̀org-toggle-custom-properties-visibility'

* org.el (org-custom-properties): New option.
(org-custom-properties-overlays): New variable.
(org-toggle-custom-properties-visibility): New command to
toggle the visibility of custom properties.
(org-check-before-invisible-edit): Also prevent errors when
trying to edit invisible properties.

Thanks to Torsten Wagner for triggering this discussion.
Merge branch 'master' of orgmode.org:org-mode

# Please enter a commit message to explain why this merge is necessary,
# especially if it merges an updated upstream into a topic branch.
#
# Lines starting with '#' will be ignored, and an empty message aborts
# the commit.
org.el: Only skip comments starting with "# " when storing a note.

* org.el (org-store-log-note): Only skip comments starting
with "# " when storing a note.

Thanks to Thomas Wallrafen for reporting this bug.
ob-R.el (org-babel-edit-prep:R): Don't set the session

* ob-R.el (org-babel-edit-prep:R): Don't set the session.

See the discussion for this issue here:
http://article.gmane.org/gmane.emacs.orgmode/58600

Thanks to Mikhail Titov and to Andrew Young for exploring it.
Revert "Makefile: add elint to compilation methods, ensure *.elc files exist after compilation"

This reverts commit 1e47e65e977e0f704feed505595ff87da0369350.