Added test for proper detection of overlapped walls.
Added ability to include json files in test descriptions.

This ability should help to encapsulate common tests
into separate test units and then include them from all
tests that need them.
Added json include file for exit code 1 tests.

Also switched all tests that would check for exit code 1 to
use this include file.

NOTE: In order for the testsuite to work properly it is necessary
to add the line

includeDir": "/absolute/path/to/nugmeg/json_includes"

to nutmeg.conf.