Replace bashisms with POSIX-compatible shell scripting.

Notably, de-duplicate '/' using a sed command from elsewhere in the same script
rather than "${name//\/\///}".

Commit by Jamey Sharp and Josh Triplett.
Signed-off-by: NJamey Sharp <jamey@minilop.net>
Signed-off-by: NJosh Triplett <josh@joshtriplett.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: NMichal Marek <mmarek@suse.cz>