MessageSourceResourceBundle overrides JDK 1.6 containsKey method, avoiding NPE in getKeys

Issue: SPR-10136
MimeMessageHelper encodes attachment filename if not ASCII compliant

Issue: SPR-9258
FreeMarkerConfigurationFactory properly supports TemplateLoaders when recreating Configurations

Issue: SPR-9389
SpringContextResourceAdapter implements equals/hashCode according to the JCA 1.5 contract

Issue: SPR-9162
Further backports from 3.2.1