Add a fork before SQL processing for non-fatal modes

This has the side-effect of hiding SQL problems and the underlying error
message. Passing the --fatal-failure flag exposes these, however.
Quote numerics inserted by SQL statements

Anything not run though DBI's quote() is now explicitly quoted inline.
Rename sqlite.schema to sqlite.sql
Make failure fatal by default; -f is now the --fork option

To make failure non-fatal, the --fork option always exits with code 0
and will fork before SQL processing. Implementations that do not wish to
deny connections when DB inserts fail would use this.

By making the fork behavior opt-in instead of opt-out, all errors are
shown by default now.