for the positive case to a separate method and used it directly from find()
and findWildcardMatch().  Moved detailed comments of findWildcardMatch to
the head of its definition so that the function body will be physically
concise.

Added utility to put messages in a message file into alphabetical
order and, for ease of further editing, the data source message file
in alphabetical order.

ones for each subcase of find().

As the concerns there seem to be false ones.

catch exception in rollback explicitly.  added a test case for that.

When we iterate and find out that there are RRs in an RRset with
different TTL, we go for the lowest of them instead of throwing and give
a warning.

added some log messages.  to make the log/exception messages useful,
also added an RRClass parameter to the Client constructor.

Some "Conn" variables were left out and forgotten in previous renames,
fixing what could be found.

and add database name to logging output

Most of the code is slightly modified copy-paste from the
Sqlite3DataSource. No documentation or log messages and the getZone
method is dummy. But it compiles and provides some kind of frame for the
rest.

Some texts of messages and parameters.