Blender Git Loki

File selector working. For now it is accessed as
context.add_fileselect(self.__operator__).

To allow file selector, I made the following changes:

- moved property definition funcs (FloatProperty, etc.) to "bpy.props"
to make them accessible from io scripts. Previously they were only
accessible in scripts running from Text Editor.

- added the "__operator__" instance attribute to py operators. The value
is RNA operator pointer.

Note that "context.add_fileselect" changes were mistakenly committed
with my last merge.