relax SVN archive

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.

Converted Scientific Python from a dependancy to an optional Python package.

Of course since this is the only PDB parser in relax at the moment, if Scientific Python is not
installed, then PDB files cannot be read.

Spun out the Scientific Python specific code into its own module.

Fixed a typo causing several unit tests to fail.

Removed many unused imports.

Added 2 unit tests for the new args of the structure.read_pdb() user function.