refactorings:
- introduced concept of default answer:
if the answer string is in the defaultish sequence, the return value of yes() will be the default.
e.g. if just pressing <enter> when asked on the console or if an empty string or "default" is
in the environment variable for overriding.
if an environment var has an invalid value and no retries are enabled: return default
if retries are enabled, next retry won't use the env var again, but either ask via input().
- simplify:
only one default - this should be a SAFE default as it is used in some special conditions
like EOF or invalid input with retries disallowed.
no isatty() magic, the "yes" shell command exists, so we could receive input even if it is not from a tty.
- clean:
separate retry flag from retry_msg
b2dedee3c8