[PATCH] replace sha1sum with sum in t/t1002

Linus,

This patch replaces sha1sum(1) with sum(1) in t/t1002. GNU sum(1) runs in "BSD
compatibility" mode by default, and not all systems have GNU coreutils. On any system
without GNU coreutils (or sha1sum) t1002 will fail. This patch should make t1002 complete
successfully everywhere that sum(1) runs.

I've tested this on Darwin and Linux; it works on both platforms.

Signed-off-by: Mark Allen <redacted>