relax SVN archive

Enabled the gnuplot format for the structure.atomic_fluctuations user function.

This uses the plotting API correlation_matrix() function for visualisation. The change allows the
Structure.test_atomic_fluctuations_gnuplot system test to pass.

Implemented a very basic gnuplot backend for the correlation_matrix() plotting API function.

This is in the new lib.plotting.gnuplot module. It creates an incredibly basic gnuplot script for
visualising the correlation matrix, assuming a text file has already been created.

Created the lib.plotting API function correlation_matrix().

This is the lib.plotting.api.correlation_matrix() function. It will be used for the visualisation
of rank-2 correlation matrices. The current basic API design here uses a dictionary of backend
functions (currently empty) for calling the backend.

Created the Structure.test_atomic_fluctuations_gnuplot system test.

This checks the operation of the structure.atomic_fluctuations user function when the output format
is set to 'gnuplot'. This will be used to implement this option. The current gnuplot script
expected by this test is just a very basic starting script for now.

Created the empty lib.plotting package.

This follows from the thread at http://thread.gmane.org/gmane.science.nmr.relax.devel/7444.

The package will be used for assembling all of the data plotting capabilities of relax. It will
make support for different plotting software - Grace, OpenDX, matplotlib, gnuplot, etc - more
coherent. This will be used to create a software independent API for plotting in relax. I.e. the
plotting software is chosen by the user and then the data output by the user function passes into
the lib.plotting API which is then passed into the software dependent backend in lib.plotting.

Implemented the lib.io.swap_extension() function.

This is confirmed to be fully functional by its four unit tests.

Created 4 unit tests for the lib.io.swap_extension function.

This is in preparation for implementing the function.

Implemented the structure.atomic_fluctuations user function.

This is loosely based on the structure.web_of_motion user function and is related to it. The user
function will write to file a correlation matrix of interatomic distance fluctuations.

Another small fix for the Structure.test_atomic_fluctuations system test.

The matrix diagonal was incorrect.

Small fix for the new Structure.test_atomic_fluctuations system test.