scan, report and trees now print one line on stderr before anything
else, naming the database and whether its path is the default or comes
from SFDUPES_DATABASE; scan also says when the file is new. report and
trees print it before opening the database, so a missing-database error
follows it. A relative path gets the working directory put in front of
it, with its symlinks resolved as the kernel reports it, and is not
cleaned: a ".." after a symlink names another file than the cleaned
path does. README "Database" lists when scan writes each file.
Unverified: the line on a terminal has no test of its own.
Model: opus-5-5