relax SVN archive

The user function data structure now accepts the 'display' boolean variable.

This is used to indicate that a user function would like to display some output to STDOUT.

Fixes for the argument checking in the auto-generated user functions.

All of the user function argument arguments are now handled by the add_keyarg() method.

All of the argument checking types are now supported for the auto-generated user functions.

This covers every type of arg_check.is_*() function used in relax.

Boolean argument types are now supported by the auto-generated GUI user functions.

The Selector_bool object and element_bool() wizard page method have been written for this.

The can_be_none user function argument argument is now used.

This is needed for proper argument checking in the auto-generated user functions.

The wizard page GetValue() method now returns None if the corresponding key is missing.

This is needed for the directory arguments as these are not shown in the GUI.

Improvements to the element_file_sel() wizard page method.

Created the special Selector_file wizard element object.

This is modelled on the file_selector() wizard page method.

Created the element_dir_sel() and element_file_sel() wizard page methods.

This will require the selector objects to be written!