relax SVN archive

Fix for the calls to the functions of the generic_fns.diffusion_tensor module.

Modified the read() function to write out all the new spins.

Fix for the test_opendx_theta_phi_da() system test.

The spin information is now loaded.

Added a check for the spin number and name being set in the vectors() function.

This must be set for the XH vector to be isolated.

Fixed a name clash of 'spin_id'.

Added a unit test to test that the Selection object has no memory of previous selections.

Fix for the RelaxSequenceError class. The pipe arg is now optional.

Created the RelaxSpinsNotLoadedError class.

Added a missing RelaxError import.

Fix for the test_opendx_theta_phi_da() system test.

The structure.vectors() user function is no longer passed the heteronuc arg.