normalize_absolute_path removes several oddities form absolute paths,
giving nice clean paths like "/dir/sub1/sub2". Also add a test case
for this utility, based on a new test program (in the style of test-sha1).
Signed-off-by: David Reiss <dreiss@facebook.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
