relax SVN archive

Made the error column optional in the loading of RDCs.

Converted the read() function from the relax_data code.

Created 2 new error classes, RelaxNoRDCError and RelaxRDCError.

Created a generic_fns rdc module by copying the relax_data module.

Converted all of the rdc user functions from the relax_data code.

Converted all instances of 'relax_data' to 'rdc'.

Converted all instances of 'ri_label' to 'id'.

Converted the rdc.read() user function from the relax_data.read() code.

Removed some debugging code.

Fix for the return_data_name() method when no match occurs and the index flag is True.