* rst.el: Use `eval-when-compile' for requiring

* rst.el: Use `eval-when-compile' for requiring
`cl.el'.  Silence compiler warnings.  Fix versions.

(rst-position-if, rst-position, rst-some, rst-signum): New
functions.
(rst-shift-region, rst-adornment-level, rst-compute-tabs)
(rst-indent-line, rst-shift-region, rst-forward-line): Use new
functions.

(rst-package-emacs-version-alist): Correct Emacs version to
represent major merge with upstream.
(rst-transition, rst-adornment, rst-compile-toolsets): Fix
versions.