Merging changes made by Arystanbek in the soc-2009-kazanbas branch, plus some things modified and added by me. * Operator exec is called execute in python now, due to conflicts with python exec keyword. * Operator invoke/execute now get context argument. * Fix crash executing operators due to bpy_import_main_set not being set with Main pointer. * The bpy.props module now has the FloatProperty/IntProperty/ StringProperty/BoolProperty functions to define RNA properties for operators. * Operators now have an __operator__ property to get the actual RNA operator pointers, this is only temporary though. * bpy.ops.add now allows the operator to be already registered, it will simply overwrite the existing one. * Both the ui and io directories are now scanned and run on startup.