relax SVN archive

Added some labelling to the infrastructure chapter of the user manual for referencing.

A number of updates and edits to the intro chapter of the user manual.

The model-free GUI screenshot has been shifted to the intro chapter in preparation for a full
tutorial with screenshots in the model-free chapter.

Updated the data model chapter of the user manual to cover the handling of protons.

This change includes the modification of the PDB reading screenshot to demonstrate the reading of a
specific model and the naming of the molecule.

All of the GUI strings and text are now formatted with a small sans serif font in the user manual.

This is because in the GUI, a sans serif font is almost always used be default.

Fix for bug #20177 (https://gna.org/bugs/?20177).

This was simply a lower precision OS/Python/numpy combination causing a test suite failure - there
are no practical effects and only the precision of the system/GUI test has been lowered.

Another bug fix for the sequence GUI editor window.

This bug was being triggered by the User_functions.test_structure_pdb_read() GUI test which now
passes.

Small fix for the User_functions.test_structure_pdb_read() GUI test.

Modified the User_functions.test_structure_pdb_read() GUI test to catch another bug.

This is a bug recently introduced with the fixes to the other sequence editor GUI window problems.

Fix for bug #20184 (https://gna.org/bugs/?20184).

The behaviour of the gui.string_conv.gui_to_int() and related functions has changed in the last few
months and the Sequence_window() GUI element has not changed to match. This has been fixed and the
User_functions.test_structure_pdb_read() GUI test now passes.

Fixes for the User_functions.test_structure_pdb_read() GUI test.