relax SVN archive

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!

Fix for bug #18789 - the zero errors in Grace files.

This was submitted by Elio Cino <ecino att uwo dott ca> at https://gna.org/bugs/?18789.

The problem was that the errors were being taken as the X-axis error values, which in the case of
spin specific data is zero. Now the Y-axis errors are taken rather than the unused X-axis errors.
This appears to have triggered a bug in the test suite relating to Grace files with both X and Y-
axis errors.

Floats are now checked in test_bug_18789 in case the Grace format changes in the future.

Created the Relax_fit.test_bug_18789() system test for catching bug #18789.

The Grace file is written out, re-opened, and then the numbers checked.

Added the script for triggering bug #18789.

This script comes from the bug report submitted by Elio Cino <ecino att uwo dott ca> at
https://gna.org/bugs/?18789.

Added some peak list files in preparation for a system test to catch bug #18789.

This data comes from the bug report submitted by Elio Cino <ecino att uwo dott ca> at
https://gna.org/bugs/?18789.

Fix for the _minimise_data_setup method introduced at r14780.

The spin_id string needs to be stored in the data_store structure.

Fix for the GuiTestResult class with the restoration of IO redirection.

The RelaxTestResult.stopTest() method is now actually called instead of the
TextTestResult.stopTest() method.

The GUI test result classes are now being used by the GUI test suite code path.