relax SVN archive

Reverted changes of the variable 'nucleus' to 'heteronucleus'.

The command used was:
svn merge -r5308:5302 ./physical_constants.py

This error was noticed by Edward d'Auvergne in a post at:
https://mail.gna.org/public/relax-devel/2008-04/msg00033.html (# Message-id:
<7f080ed10804040741x3e26f862r808982451ab522c8@...>)

Added a string used to identify the structural object.

Updated the methods of the Scientific Python PDB specific structural object class.

These now use the structure of the new object.

Partially fixed more of the code so the Jw mapping system test can go further before failure.

Re-introduced the test for the existence of the current pipe and correcte a comment.

Changed the parser specific data object name to 'structural_data' and initialised it to [].

Partially fixed the code so the Jw mapping system test can go further before failure.

Bug fix for the system test for the loading of the sequence from a PDB file.

Added a module docstring.

Created the Scientific Python specific data object.

The functions specific to Scientific Python have been converted into methods of the object. The new
object inherits from api_base.Str_object.