renamed ObjectsDb -> ObjectDb
added test to UnmarshallerTest
added WritingHashedObjectFailedError
removed unused SandboxImpl.objectDb()
refactored Unmarshaller to not throw FileSystemException but proper errors
refactored HashedDb to report ReadingHashedObjectFailedError instead of FileSystemError
added ObjectDbError
improved messages in .object.err.* errors
moved DuplciatePathError to .task.base.err
moved FileBuilder/FileSetBuilder -> .plugin.api
added CannotAddDuplicatePathError and refactored FileSetBuilder to use it
refactored FileSetBuilderTest
removed unused MutableStringSet
moved EmptySet to inside of Type class
moved File/FileSet/StringSet .type.api -> plugin.api
renamed .plugin.api -> .plugin
moved classes type.impl.* -> plugin.* in testing tree
removed unused StringUtils
moved StreamTester.inputStreamToString() to Streams
merged .fs.base.Streams with .util.Streams