relax SVN archive

Changes to the internal structural object.

The _parse_models_pdb() method has been renamed to _parse_pdb_coord() and the opening of the PDB
file shifted into the base load_pdb() method. This is in preparation for better parsing of PDB
files to match the main sections of the PDB format, see
http://www.wwpdb.org/documentation/format33/v3.3.html.

Added the full 1UBQ PDB structure to the relax test-suite shared data directories.

This is a small, very quick to read structure which will be used for validating the reading and
writing of different PDB record types.

Fix for the unit tests of the generic_fns.structure package.

The _parse_pdb_record() is now covered by the new pdb_read module, so its unit tests have also been
shifted into a new module.

Created the generic_fns.structure.pdb_read module.

This replaces the internal structural object _parse_pdb_record() method which was handling both
ATOM+HETATM and CONECT records. It should allow greater flexibility in reading data out of other
PDB records in the future. There is one function per PDB record type in this module.

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.