set source and target compatibility to 1.7 for now to make the Groovy
compiler happy
fix singleton property assignment

The bean builder supports a syntax that allows the "singleton" property of the bean configuration to be assigned a boolean.  Prior to Spring 4 this worked because AbstractBeanDefinition.setSingleton() existed.  That method has been removed in Spring 4 so we need special handling to support the same syntax in the bean builder.