Merge branch 'jk/test-send-sh-x-trace-elsewhere'

Running tests with '-x' option to trace the individual command executions is a useful way to debug test scripts, but some tests that capture the standard error stream and check what the command said can be broken with the trace output mixed in. When running our tests under "bash", however, we can redirect the trace output to another file descriptor to keep the standard error of programs being tested intact. * jk/test-send-sh-x-trace-elsewhere: test-lib: set BASH_XTRACEFD automatically