Enhance sqlite3_rsync so that, by default, it will sync non-WAL-mode

Enhance sqlite3_rsync so that, by default, it will sync non-WAL-mode
database files.  Add a new command-line option --wal-only that restricts
the sync to WAL-mode databases only (the former default).  Improve
command-line option parsing so that only a single "-" is required before
each option.

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