Sets some tags and provides gadget specific data. Prefer this to
SetAttrsA(), if you are manipulating gadgets.
INPUTS
gadget
Change the attributes of this gadget
window
The window of the gadget
requester
The requester of the gadget (or NULL)
tagList
This is a list of attribute/value-pairs
RESULT
Depends in the class. For gadgets, this value is non-zero if
they need redrawing after the values have changed. Other classes
will define other return values.