* plugins/*/*.[ch]: Use class macro for type casting (ANJUTA_PLUGIN_*).

	* libanjuta/anjuta-plugin.h: Modification of the ANJUTA_PLUGIN_BEGIN
	macro so that the generated function support a NULL plugin parameter.

	* plugins/debug-manager/debug_tree.c: Fix an incorrect call to gfree
	in debug_tree_find_expression by freeing memory returned by the call
	to gtk_tree_model_get instead of the parameter string.