ca-shell.c: Make readline ignore escape sequences in prompt

Without this patch, readline is unable to determine the real printed length of
the prompt, and line editing ends up botching its appearance.

Signed-off-by: Morten Hustveit <morten.hustveit@gmail.com>
Reload schema at the first data statement in a transaction

If the schema is not reloaded, we risk working on a stale copy.  Locking will
ensure that the schema doesn't become stale while we're working on it.

Due to how frequently this operation must be performed, we should later add
optimizations to ensure a schema isn't reloaded when it hasn't been changed,
and make the parsing of the schema as fast as it can possibly be.

Signed-off-by: Morten Hustveit <morten.hustveit@gmail.com>
schema.c: Truncate table upon creation

This removes the old capability of adding an existing table to the database.
Changing this behavior will make it simpler to replace an existing table
without creating a new file; see the next commit.

Signed-off-by: Morten Hustveit <morten.hustveit@gmail.com>
Added the VOLATILE transaction level

Changes made in a VOLATILE transaction may become immediately visible in other
transactions, regardless of their isolation levels.  This mode is only added
for performance reasons.

Signed-off-by: Morten Hustveit <morten.hustveit@gmail.com>