elisp-common.eclass: New function elisp-check-emacs-version.

elisp-common.eclass: New function elisp-check-emacs-version.

Tests if the Emacs version is at least the (full) version specified
by NEED_EMACS, otherwise dies. Intended as a replacement for function
elisp-need-emacs, which did only a simple numeric comparison of the
major version.

Call the new function before doing any actual work in elisp-compile()
and elisp-make-autoload-file(), so ebuilds inheriting only
elisp-common.eclass (but not elisp.eclass) won't have to add a
pkg_setup phase function.

Drop support for EAPIs 0 to 3.

Signed-off-by: Ulrich Müller <ulm@gentoo.org>