Returns the verbosity level from option, environment variable, or default.
Checks in order: ggseg.extra.verbose option, GGSEG_EXTRA_VERBOSE env var,
then defaults to 1L.
Returns the verbosity level from option, environment variable, or default.
Checks in order: ggseg.extra.verbose option, GGSEG_EXTRA_VERBOSE env var,
then defaults to 1L.