* gnus-agent.el (gnus-agent-cat-name): Eval macro while compiling.

	* gnus-agent.el (gnus-agent-cat-name): Eval macro while compiling.
	(gnus-agent-cat-disable-undownloaded-faces): New function.
	Accessor for new agent property
	'agent-disable-undownloaded-faces'.
	gnus-cus.el (gnus-agent-parameters): Added
	agent-disable-undownloaded-faces and corrected documentation.
	(gnus-agent-cat-prepare-category-field,
	gnus-agent-customize-category): Changed to avoid creating free
	references to each field's symbol.
	gnus-sum.el (gnus-summary-use-undownloaded-faces): New local variable.
	(gnus-select-newgroup): Initialize it.
	(gnus-summary-highlight-line): Use it.