relax SVN archive

Fixes for the extract() function.

Reintroduced the test for the model-free model but with a RelaxError now thrown.

This test was important as the model is necessary to differentiate between te and ts in the mfout
file!

Removed the tests in extract() for the presence of a model-free model and relaxation data.

These tests reduce flexibility as these can be set later, and the reading of the mfout file does not
depend on these.

Fixed the call to line_positions().

Converted the line_positions() to the new design.

Removed all references to 'self' in the extract() function.

Removed all references to 'self' in the create() function.

The mkdir() function is now called relax_io.mkdir_nofail().

Fixed the usage of the relax_io module.

Replaced the redundant module function open_file() with relax_io.open_write_file().