Overhaul SQL error logging.
Use the primary sqlite3 interface for error logging, using a callback
function to report any errors as they happen. This will allow us to
interface directly to the database if necessary rather than having to go
via the pkgindb_doquery() interface, and also provides useful error
messages rather than the very unhelpful "callback aborted".
Update the log output to include the date, format better for
readability, and open in append mode so we don't potentially lose useful
errors.
While here reorganise some functions into logical order and move the
remaining function declarations to pkgin.h
UnifiedSplitRaw
