variable 7.x-1.0-beta2

Simplified hooks and added documentation.

45f5d01 Added 'required' property to simplify form elements. Cleaned up node variables.
96d6a95 Added documentation, some more comments, and cleaned up system variables.
d9061c0 Marked some more variables as localizable. Removed unused hooks.
b0de7bc Removed obsolete select_country variable type. Fixed some comments.
8cc20bd #1073834 Reduce realm key field length so it can be used on the primary key
01828aa Added child variable information and form generator for node types. Reorganized some functions so they can be invoked by other modules.
fdf0c4b Unified hook_type_info() and hook_option_info(). Unified callbacks so they all take a as first argument.
9b139f5 Added variable_callback() and 'options' attribute for list of options
8ebb0f1 Added date formats
2582093 Fixed #1072440, Ancient variables defined