use cl- prefixed symbols from cl-lib.el

instead of the prefix-less variants from cl.el

Conflicts:
	magit.el
don't use cl-flet

The forward-compatibility cl-lib does not define it.  Instead use let
and funcall (2x) or refactor so that tempory overriding function
definitions are not needed (1x).
require cl-lib at runtime, suppress warnings

Suppress the "cl package called at runtime" warning in Emacsen before
24.3, using `with-no-warnings`.  When doing that would me more hideous
than replace the cl function with a non-cl replacment, then do the
latter.
use cl-do instead of do
use cl-find-if instead of depending on implicit block

On Emacs-24.2.93 that block does not exist for some reason,
causing an error.
fix bug introduced in 361f2d6

implement acons with cons, not nconc
Merge branch 'tarsius/cl-lib'

Conflicts:
	magit-svn.el
	magit.el