GUAC-969: Fix possible NPE in GuacamoleClassLoader, if the contents of the lib directory cannot be listed.
GUAC-969: Test filters can be static.
GUAC-969: Fix possible NPE in XML parsing.
GUAC-969: Fix possible NPE in reading of local environment.
GUAC-969: Remove unused variables.
Merge pull request #34 from glyptodon/fix-static-defects

GUAC-969: Fix defects from recent static analysis.