relax SVN archive

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.

Renamed the J(w) mapping specific set() method to set_doc().

The base class method set() is used instead.

Updated the J(w) mapping code to handle a spin system specific 'nucleus' variable.

The specific value setting function, of the base class, now handles string values.

Fixed all the unit tests of setting the heteronucleus type.

The variable will be called 'nucleus' and not 'heteronuc'.