relax SVN archive

Ported r2924 to r2927 from the 1.3 line.

The command used was:
svn merge -r2923:2927 svn+ssh://bugman@.../svn/relax/1.3

This adds a few features to the selection user functions. For the the 'select.read()' and
'unselect.read()' user functions a different column for the residue numbers can now be specified.
The 'select.res()' and 'select.read()' now accept the boolean keyword option which can be set to
'OR', 'NOR', 'AND', 'NAND', 'XOR', or 'XNOR'. The default, and previous behaviour, is 'OR'.

Added a sample script to create a LaTeX longtable of the model-free results.

Spin systems can now be selected using boolean operators.

The user functions 'select.res()' and 'select.read()' now accept the boolean keyword option which
can be set to 'OR', 'NOR', 'AND', 'NAND', 'XOR', or 'XNOR'. The default, and previous behaviour, is
'OR'.

The selection user functions which read data from a file now take header lines into account.

Bug fix, the 'self.sel_read()' function was not expecting the 'column' argment.

You can now specify a different column for residue numbers in the selection user functions.

This affects both the 'select.read()' and 'unselect.read()' user functions.

Addition of the user function 'structure.vector_dist()'.

This function will display the PDB representation of the XH vector distribution overlain over the
macromolecular structure within PyMOL.

Created a symmetric chain 'B' in the PDB representation of the XH vector distribution.

Added the ability to create ATOM PDB records within the 'self.write_pdb_file()' method.

Changed the format of the PDB representation of the XH vector distribution.

Each XH pair is being created as a proper vector with two atoms rather than all protons connecting
back to a single centre of mass.