As recommended by http://static.springsource.org/spring/docs/3.0.x/spring-framework-reference/html/mvc.html#mvc-static-resources I wish to use
Attributes in <mvc:resources>
were added in Spring 3.0.4.
EDIT That is: you just add Spring 3.0.4 to your dependencies and everything works fine (except error marks in Eclipse plugin). At runtime config files are parsed by Spring itself, therefore Spring's built-in XSD file is used.
Not better than axtavt's response, but a little clue on how to suppress Eclipse error. Go into the Project properties and then Spring→Beans Support→Load NamespaceHandlers and XSDs from project's classpath [experimental]: