This introduces a new fs.Option flag, Sensitive and uses this along
with IsPassword to redact the info in the config file for support
purposes.
It adds this flag into backends where appropriate. It was necessary to
add oauthutil.SharedOptions to some backends as they were missing
them.
Fixes#5209
This is possible now that we no longer support go1.12 and brings
rclone into line with standard practices in the Go world.
This also removes errors.New and errors.Errorf from lib/errors and
prefers the stdlib errors package over lib/errors.
- setup correct path encoding (fixes backend test FsEncoding)
- ignore range option if file is empty (fixes VFS test TestFileReadAtZeroLength)
- cleanup stray files left after failed upload (fixes test FsPutError)
- rebase code on master, adapt backend for rclone context passing
- translate Siad errors to rclone native FS errors in sia errorHandler
- TestSia: return proper backend options from the script
- TestSia: use uptodate AntFarm image, nebulouslabs/siaantfarm is stale
