test-framework-sh: minor cleanups * tests/init.sh (testdir_prefix_): Output a trailing newline, since strictly speaking POSIX requires this. (setup_): Do not use the variable 'fail', as that makes the trace output harder to read ('fail' is typically used by tests to mean the test failed). Treat // portably. Check that new directory is not merely a sibling of the tmp dir. Avoid unnecessary invocation of tr.