#37 check exit code of debugger

[Nicholas Bamber]

The test scripts run bashdb against a script
and feed commands to the bashdb process, and compare
the output against the expected output. What the upstream
test code does not do is check the exit status of the bashdb
process. If it is not 0 that should be a test failure.
This patch fixes that by parsing the exit code and appending that
to the test output, which will cause the output to not match
against the expected output.

[Rocky Bernstein]

Bug seems to exist in bash 4.3 but is fixed in bash 4.4. See https://lists.gnu.org/archive/html/bug-bash/2015-10/msg00219.html . However I'll code around this in the test for bash 4.3.