Ignore .DS_Store files
Show an alternative property page if JVM version is less than 7

If Eclipse runs on a JVM with version less than 7, the eclipse-pmd
plug-ins will not be started. This change adds another plug-in that
starts if the JVM version is at least 1.3 and shows an alternative
project property page if the JVM version is less than 7. This resolves
#6.