relax SVN archive

Shifted the read_spin_data() and write_spin_data() functions from lib.io to lib.sequence.

Removed a number of unused imports from the user function definitions.

These unused user_function package imports were found using the find_unused_imports.py development
script.

Shifted the pipe_control.sequence.validate_sequence() function into the relax library.

For this, the new lib.sequence module has been created. This change is for better library
independence. A circular import with lib.io and lib.arg_check has also been resolved.

Shifted the Python 2 and 3 compatibility module 'compat' into the relax library.

Improvements to the test_library_independence.py development script.

This script for checking the independence of the relax library will now recursively import all
packages and modules in the library and report at the end a list of all failures.

Removal of all unused imports in the lib.dispersion package.

Added a script for testing the independence of the relax library.

Removed the dependency on the relax dep_check module from the relax library.

This is to further decouple the library from relax.

Divide by zero avoidance fix for the rotor frame order model module lib.frame_order.rotor.

Improved support for printing stack tracebacks with RelaxWarnings.

The '--traceback' command line option will now show a full traceback. A replacement
warnings.showwarning() function has been written to write out the traceback before the
warnings.formatwarning() replacement function is called.