tests: skip test_eval_ in internal chain-lint

To check for broken &&-chains, we run "fail_117 && $1" as a test snippet, and check the exit code. We use test_eval_ to do so, because that's the way we run the actual test. But we don't need any of its niceties, like "set -x" tracing. In fact, they hinder us, because we have to explicitly disable them. So let's skip that and use "eval" more directly, which is simpler. I had hoped it would also be faster, but it doesn't seem to produce a measurable improvement (probably because it's just running internal shell commands, with no subshells or forks). Note that there is one gotcha: even though we don't intend to run any of the commands if the &&-chain is intact, an error like this: test_expect_success 'broken' ' # this next line breaks the &&-chain true # and then this one is executed even by the linter return 1 ' means we'll "return 1" from the eval, and thus from test_run_(). We actually do notice this in test_expect_success, but only by saying "hey, this test didn't say it was OK, so it must have failed", which is not right (it should say "broken &&-chain"). We can handle this by calling test_eval_inner_() instead, which is our trick for wrapping "return" in a test snippet. But to do that, we have to push the trace code out of that inner function and into test_eval_(). This is arguably where it belonged in the first place, but it never mattered because the "inner_" function had only one caller. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>