Make "git log" exit properly if not in a git archive

Instead of getting an incomprehensible error message from git-rev-list.

git-log-script

@@ -1,2 +1,3 @@
 #!/bin/sh
+. git-sh-setup-script || die "Not a git archive"
 git-rev-list --pretty $(git-rev-parse --default HEAD "$@") | LESS=-S ${PAGER:-less}