Supplant the "while case ... break ;; esac" idiom

Supplant the "while case ... break ;; esac" idiom

A lot of shell scripts contained stuff starting with

	while case "$#" in 0) break ;; esac

and similar.  I consider breaking out of the condition instead of the
body od the loop ugly, and the implied "true" value of the
non-matching case is not really obvious to humans at first glance.  It
happens not to be obvious to some BSD shells, either, but that's
because they are not POSIX-compliant.  In most cases, this has been
replaced by a straight condition using "test".  "case" has the
advantage of being faster than "test" on vintage shells where "test"
is not a builtin.  Since none of them is likely to run the git
scripts, anyway, the added readability should be worth the change.

A few loops have had their termination condition expressed
differently.

Signed-off-by: David Kastrup <dak@gnu.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>