Rename variables and functions with "auto-load" in their names

Rename variables and functions with "auto-load" in their names

* doc/emacs/building.texi (Lisp Libraries): Adjust documentation.

* lisp/help-fns.el (help--symbol-completion-table): Adjust usage.

* lisp/help-fns.el (help-enable-completion-autoload): Change name
from auto-load and declare an obsolete alias (bug#13418).

* lisp/help.el (help-enable-autoload): Ditto.

* lisp/progmodes/vhdl-mode.el: Ditto.
(vhdl-create-mode-menu, vhdl-mode): Adjust usage.
(vhdl-autoload-project): Rename from auto-load and declare an
obsolete alias.