git-svn: exit with status 1 for test failures

Some versions of the SVN libraries cause die() to exit with 255,
and 40cf043389ef4cdf3e56e7c4268d6f302e387fa0 tightened up
test_expect_failure to reject return values >128.

Signed-off-by: Eric Wong <normalperson@yhbt.net>
Signed-off-by: Junio C Hamano <junkio@cox.net>