relax SVN archive

Wrote 16 unit tests for all args of all structure user functions.

Modified the structure.vectors() user function to use the spin_id string.

It was previously using the residue number and name id system.

Converted all the 'structure' user functions to the new relax design.

Bug fix for the value arg unit test of the value.set() user function.

The valid str arg types are now being caught and skipped.

Updated the value arg unit test of the value.set() user function to use another new RelaxError.

Added a missing RelaxError import.

Updated the value arg unit test of the value.set() user function to use the new RelaxError.

Updated the value.set() user function to accept string values of the 'value' variable.

Two new RelaxErrors have been created for this.

Bug fix for the base class value setting method set().

If no default value exists, this is now caught and a RelaxError is thrown.

Updated the value.set() user function to use the correct J(w) mapping value setting docstring.