[PATCH] Guilt: Replace print_usage and exit 1 with usage and die in git-sh-setup

[PATCH] Guilt: Replace print_usage and exit 1 with usage and die in git-sh-setup

git already has utility functions for shell script porcelains.  use
them instead of implementing our own.

[jsipek: Don't source git-sh-setup in guilt-*, just guilt]
Signed-off-by: Yasushi SHOJI <yashi@atmark-techno.com>
Signed-off-by: Josef 'Jeff' Sipek <jsipek@cs.sunysb.edu>