t1006: prefer shell loop to awk for packed object sizes

To compute the expected on-disk size of packed objects, we sort the output of show-index by pack offset and then compute the difference between adjacent entries using awk. This works but has a few readability problems: 1. Reading the index in pack order means don't find out the size of an oid's entry until we see the _next_ entry. So we have to save it to print later. We can instead iterate in reverse order, so we compute each oid's size as we see it. 2. Since the awk invocation is inside a text_expect block, we can't easily use single-quotes to hold the script. So we use double-quotes, but then have to escape the dollar signs in the awk script. We can swap this out for a shell loop instead (which is made much easier by the first change). Signed-off-by: René Scharfe <l.s.r@web.de> Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>