Display canonicalized file names on copy errors
Fix checker exit code processing
Refactor checker exit code processing
Move required_fields from global constants to Spawner module
CATS::Spawner: remove useless code and fix whitespace
Spawner: Centralize calls to chdir, fix direcory after report parsing error
Extract get_testset to Judge::Server

+ Remove ugly workaround for dummy testsets
Judge::Dummy: fix syntax, whitespaces, test output