relax SVN archive

Shifted the calculation of the uniform sphere point positions into angles_uniform().

This removes this replicated code from various functions, allowing for more flexibility.

Converted generate_vector_dist() to use a limit checking function and simplified the code.

The angle arrays are now returned by uniform_vect_dist_spherical_angles() so that
generate_vector_dist() can use any spherical point distribution. The max_angle arg has been changed
to limit_check so that any type of vector distribution can be created.

The limit_check() method has been added to the cone objects to determine if a point is inside or not.

Added a new cone type in the Pseudo_elliptic class.

The frame order and N-state model cone_pdb() methods now use the isotropic cone object.

The cone_edge() method now calls a function to obtain the maximum polar angle.

The cone_edge() arg 'angle' has been changed to 'phi_max_fn'.

Added a new module for holding class objects defining different cone types.

This currently contains the Iso_cone class with the simple method phi_max() to return the cone edge.

Removed the pipe test from the pymol.cone_pdb() user function.

This check is not necessary as a data pipe is not needed for this.

Fix for the N-state model user function n_state_model.cone_pdb().

This was not calling the correct method.

Bug fix for the N-state model cone PDB creation _cone_pdb() method.

The internal structural API had changed. structure.add_struct() is now called
structure.add_molecule().