DrJavaRoot.LANGUAGE_LEVEL_EXTENSIONS so that they are compatable
with IOUtils.extensionFilePredicate(). In MainFrame, they have
been manually added back where they were removed.
M src/edu/rice/cs/drjava/DrJavaRoot.java
M src/edu/rice/cs/drjava/model/AbstractGlobalModel.java
M src/edu/rice/cs/drjava/ui/MainFrame.java