relax SVN archive

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!

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.