[deployment] Meta-command support in deployment script

Imported From: http://groups.google.com/group/in-portal-dev/browse_thread/thread/c467fccb10e25818#

In In-Portal 5.1.3 new deployment script functionality was developed. It allows to:

• specify revision-based database queries
• revision dependencies

After missing (revisions that weren't executed before) are executed these actions are performed:

• resets caches
• import language pack

This very powerful already, but it missing ability to execute a revision-specific php code.

I see this as a meta tags, placed inside a comments, like this:

# {namespace:meta_tag_here}

There also can be several meta-tags per line. When processed we'll scan all registered namespaces and then ask them to process meta tag.