Manage reftex's internal autoloads automatically

Manage reftex's internal autoloads automatically

* lisp/textmodes/reftex.el: Manage most autoloads automatically.

* lisp/textmodes/reftex-auc.el, lisp/textmodes/reftex-cite.el:
* lisp/textmodes/reftex-dcr.el, lisp/textmodes/reftex-global.el:
* lisp/textmodes/reftex-index.el, lisp/textmodes/reftex-parse.el:
* lisp/textmodes/reftex-ref.el, lisp/textmodes/reftex-sel.el:
* lisp/textmodes/reftex-toc.el: Set generated-autoload-file,
and add autoload cookies for reftex.el.

* lisp/Makefile.in (AUTOGEN_VCS): Add textmodes/reftex.el.