relax SVN archive

Added compiling of the relaxation dispersion C code as scons default and added dependency checks.

More work is needed, sucha as, obviously, the modification of the c code itself to suit relaxation
dispersion needs.

Corrected an error introduced in r8704 where the __init__.py file for system tests was modified for
the purpose of fast testing while coding...

Copied C files for Rx curve fitting for adapting as the code for dispersion curve fitting.

The new files will need a lot (!) of modifications to meet the needs of relaxation dispersion.

The commands used were:
svn cp maths_fns/relax_fit.h maths_fns/relax_disp.h
svn cp maths_fns/relax_fit.c maths_fns/relax_disp.c
svn cp maths_fns/exponential.h maths_fns/dispersion.h
svn cp maths_fns/exponential.c maths_fns/dispersion.c

Updated a few dosctrings and tried to improve the system test.

Started to implement the reading of 'r2eff' by relax_data.read() by first writing a system test.

Created a module for calculating different optimisation/energy potentials.

The function quad_pot() has been written to provide a flat-bottom potential.

Added a call to calc() to test the quadratic potential calculation.

Fixed the unit tests.

This is as proposed by Ed in a post at:
https://mail.gna.org/public/relax-devel/2009-01/msg00132.html
(Message-id: <7f080ed10901280921t21fa4c3bpf70440d4c7a835b5@...>)

Thanks Ed !

Fixed a bug which prevented the manual pdf to be compiled.

The problem was caused by a ':' character in the references (after the volume number, as usual).
This was changed for a '.' character.

Equations were fine..!

Moreover, a better formatting was done by adding ':' characters after the word 'are' before
enumerations.

Started to make changes for multiple field relaxation disperison analysis.

This seems necessary, so maybe we should not support single field analysis of relaxation dispersion
at all.

-> Kovrigin et al. (2006) JMagRes, 180: 93-104.

...

The changes made here are only a first draft and may not work. In particular, maybe the
spectrum.read_intensities(), relax_disp.cpmg_frq(), spectrum.replicated(),
spectrum.error_analysis(), and deselect.read() functions will need to know the magnetic field to
which the particular dataset is associated...

In fact, the different datasets should be input first and their R2eff calculated indepentantly. In
a second step, the actual relaxation dispersion curve fitting should be made with all data.