When the ClassUpdater finds a file that ends in
".class" but isn't a valid Java class file, it
logs a long, scary exception.  Exceptions are
supposed to be used for occasional occurrences,
but we cannot assume that the content of all files
whose names end in ".class" are guaranteed to be
Java files.  At most, a "invalid class file:
<filename>" message should be logged instead of
the exception.

To recreate, copy any data file to something like
"foo.class" in a project directory to create a bad
class file.  

Suggested fix:  the classfile module can define an
InvalidClassFormatException which extends
IOException, and throw that for those cases where
it detects a bad class format.  ClassUpdater can
separately catch this exception, and either log
the bad file by name, or ignore it.  This way,
real IOExceptions (bad disk, etc.) can still be
logged.  I'd be happy to make these changes.