relax SVN archive

Formatting fixes for the generic_fns.structure.pdb_write module.

Added a new module generic_fns.structure.pdb_write for generating the PDB records.

This decouples the formatting code from the internal structural obect. The PDB format has been
updated to version 3.30. There is one function for each PDB record, allowing this to be easily
extended and kept up to date.

Created the Structure.test_rmsd_ubi system test to better check the structure.rmsd user function.

This uses the truncated ubiquitin ensemble in the test suite shared data directories. The RMSD
matches the VMD 1.9.1 output.

Printout improvements for the structure.rmsd user function.

Updated the generic_fns.structure package __all__ variable to include the statistics module.

Created a new float_object argument type which is used by the 'pos' argument of structure.add_atom.

A new arg_check.float_object() function has been created to handle any float object greater than
rank-0.

Fixes for the Structure.test_rmsd system test - it now passes.

Implemented the structure.rmsd user function.

Docstring addition for the generic_fns.structure.statistics.atomic_rmsd() function.

Fix for the structure.add_atom user function for the internal structural object.

The atomic positions for each model are now correctly set.