checklink: degrade gracefully on posix when fs is readonly (issue5511) In the unlucky case, checklink tries to make a new file for the symlink test to target. If the filesystem is readonly (perhaps due to permissions in a repo owned by someone else) we just report the filesystem as not supporting symlinks, since the user probably can't write anyway.

revlog: remove some revlogNG terminology RevlogNG is not such a good name when it is no longer the newest revlog version. Since we'll soon have revlog version 2, let's remove some references to it.

revlog: tweak wording and logic for flags validation First, the logic around the if..elif..elif was subtly wrong and sub-optimal because all branches would be tested as long as the revlog was valid. This patch changes things so it behaves like a switch statement over the revlog version. While I was here, I also tweaked error strings to make them consistent and to read better.