fixed python script

all these variables are not defined and have to be extracted from `test`.

Running the script this way resulted in error:

```
python cmm/test/spec_tests.py --spec cmm/spec.txt --program "./bin/markdown --flavor=common"
Traceback (most recent call last):
  File "cmm/test/spec_tests.py", line 137, in <module>
    if do_tests(cmark, tests, args.pattern, args.normalize):
  File "cmm/test/spec_tests.py", line 114, in do_tests
    result = do_test(test, normalize)
  File "cmm/test/spec_tests.py", line 47, in do_test
    print_test_header(headertext, example_number,start_line,end_line)
NameError: global name 'headertext' is not defined

```
make the diff output work
Merge pull request #229 from cebe/fixed-python-script

fixed python script