relax SVN archive

Modified the new test_rdc_tensor() N-state model system test to not produce files.

Created the N-state model test_rdc_tensor() system test for catching a strange RDC back calc bug.

Bug fix for a newly introduced dependency on the wxPython module.

This wx module is now optional, and only required for the GUI mode. This allows relax to run
without this module installed.

Bug fix for IO capture in the test suite with Python 2.6 or below.

The RelaxTestRunner._makeResult() replacement method has been reinstated. Replacing the class
variable resultclass does not work with earlier versions of the unittest site-package.

Bug fix for the test suite for Python 2.6 and below, introduced at r14788.

The unittest.TextTestResult class only exists in Python 2.7 and above!

Fix for bug #18790 - the negative relaxation data errors.

The cause of this is unknown, as similar data is already checked in the test suite. Now the
relaxation data is not looked at if it or its error is None. This type of data worked perfectly
before! A very strange bug!

Created the Mf.test_bug_18790() system test for catching bug #18790.

Added the script for triggering bug #18790.

This script comes from the bug report submitted by Vitaly Vostrikov <vvostri att gmail dott com> at
https://gna.org/bugs/?18790.

Added some relaxation data files in preparation for a system test to catch bug #18790.

This data comes from the bug report submitted by Vitaly Vostrikov <vvostri att gmail dott com> at
https://gna.org/bugs/?18790.

Fix for the bug introduced in r14797 for the xydxdy Grace plots.

Two if statements are needed, not an if-elif block!