[emacs] Remove "l" binding from `help-mode-map'

The trunk version of Emacs has "l" bound to `help-go-back' in
the `help-mode-map'.  See [1].

[1] http://debbugs.gnu.org/cgi/bugreport.cgi?bug=16178
Update copyright notices
[emacs] Add notmuch autoload only if mail.el file exists

If there's no ~/.emacs.d/mail.el file then there's no configuration
for notmuch anyway so there's no point in adding autoload for it.
[emacs] Remove bunch of compatilibity code

I'm living on a bleeding edge and for years did not have to use
an old version of Emacs so that code is not really necessary for
me.  More importantly though, it undergoes no testing what so
ever, so there's no guarantee it is correct.
[emacs] Remove `setq-if-bound' macro

It wasn't really necessary for anything to be honest.
[emacs] `caddr' and `cdddr' are not defined, so fix the code

It seems only two-levels of c[ad][ad]r functions are defined
in Emacs Lisp, so `caddr' and `cdddr' are not present.  Fix
the code by open-coding the more-complex functions using the
shorter ones.
[emacs] When finding `user-init-file' be aware it may point to .elc file

The `user-init-file' may point to a byte-compiled Emacs Lisp file
so when finding it, make sure .el is used instead of .elc.
[emacs] Add more `org-mode' customisation