Performance: Suspend cache invalidation.

Track queries, time. Fire actions to allow for environment-specific
adjustments like sending DB reads to masters, autocommit=0, etc.
Add filename being processed to line output.
Skip duplicate and undocumented hooks.
Use :: as a class::method delimiter.
Ignore items with @ignore tags.
Avoid queries with update_post_meta().

Non-strings fail the test in update_metadata() where get_metadata()
is used to see if an update is needed.
Use the indexed slug field to find existing items.
Add insert_term method to simplify/reduce queries.
Remove transition post callbacks for performance.
Avoid unnecessary post update calls (part 1).
Avoid boatloads of term and post queries.

Simplify and centralize term creation to avoid repeated term_exists().
Watch for changes to terms and meta before deciding whether to update
the post. (Updating the post bumps post_modified, which we do want,
but don't want on every import.)

Also fixes package/subpackage assignments which were overwriting each
other.
Merge pull request #104 from nacin/speed

Performance improvements and various fixes