relax SVN archive

Simplified the chi2 gradient unit test and added delete statements to destroy all unit test data.

Added a tearDown statement to delete the chi-squared Hessian.

More docstring improvements for the chi-square function unit tests.

Added a unit test for the chi-squared Hessian function d2chi2.

Improvements to the docstrings and a comment in the chi-squared value and gradient unit tests.

Replaced the empty chi2 and dchi2 unit tests with true unit tests for those functions.

Removed the line '#!/usr/bin/env python' from all the unit test modules.

Removed the svn:executable property from the 'maths_fns/test_chi2.py' unit test file.

Fixed the test suite synopsis (the system/functional tests weren't returning the test result).

All the contents of the System_tests.__init__() method has been placed into the run() method as
__init__() needs to return None. This run() method then returns the global_pass flag to the
Test_suite_runner class or test_suite/runner.py.

improved messages for bad input