minirst: refactor/simplify findblocks

inotify: raise correct error if server is already started in a deep repository When path is too long to be an Unix socket address, we create a socket in a temporary directory and link from the long path to the shorter one. But checks in server code at startup were insufficient in this case, and used to raise an unclear "tried linking .hg/inotify.sock to a temporary socket but .hg/inotify.sock already exists"