creating audit trigger

[zevbo]

This commit has all of the changes I have made creating the audit trigger. The behavior of the audit trigger is documented on the update to the trigger documentation page in this commit.

This commit also has the creation of sc_chain_next (which may eventually be merged with sc_next). sc_chain_next is a field in the schema change type struct which represents a linked list, and osqlcomm will automatically execute all schema changes in that linked list in osql_process_schemachange.

As of now, audit trigger has no time part functionality. Also, the chained alters are by default disabled. This is mainly because triggers don't yet automatically expand to new fields.

[riverszhang89]

Please /runtests for Zev.

[nirbhayc]

/plugin-branch feature-final