[ANN] Remove XEmacs compatibility layer

[Nicolas Goaziou <mail@nicolasgoaziou.fr>]

Hello,

I finally did the grunt job and removed all XEmacs compatibility in the
code base (development branch).

On the Emacs side, the following functions are now considered obsolete
and may trigger innocuous compilation warnings:

- `org-add-hook',
- `org-decompose-region',
- `org-detach-overlay',
- `org-file-equal-p',
- `org-float-time',
- `org-indent-line-to',
- `org-indent-to-column',
- `org-looking-at-p',
- `org-looking-back',
- `org-match-string-no-properties',
- `org-propertize',
- `org-re',
- `org-select-frame-set-input-focus'

The next step is to remove compatibility code for Emacsen older than
24.3 release, if anyone feels like spending some time on it during
a rainy day.

Regards,

-- 
Nicolas Goaziou                                                0x80A93738