- implement updating exit code based on severity, including modern codes
- extend print_warning with kwargs wc (warning code) and wt (warning type)
- update a global warnings_list with warning_info elements
- create a class hierarchy below BorgWarning class similar to Error class
- diff: change harmless warnings about speed to rc == 0
- delete --force --force: change harmless warnings to rc == 0
Also:
- have BackupRaceConditionError as a more precise subclass of BackupError
If not set, it will default to "legacy" (always return 2 for errors).
This commit only changes the Error exception class and its subclasses.
The more specific exit codes need to be defined via .exit_mcode in the subclasses.
This not only brings code style in line with the other helpers that do the
same thing this way, but also does away with an unnecessary absolute import
using the borg module name explicitly.