[development] Help add descriptions to the schema table definitions

[Barry Jaspan]

schema.module now supports displaying documentation included in the
schema data structure as specified in
http://drupal.org/node/146939. We should add this information for all
core tables. There are 64 such tables so if a handful of developers
document the tables they are most familiar with it will all get done
very quickly.

So, please choose a core module or two and document its tables.  To
avoid having many people trying to edit the same patch file, add your
docs to the issue: http://drupal.org/node/160599.

I will combine all responses into a single patch. The patch will
change the .schema files but only by adding documentation so I assume
this will be acceptable even in code freeze.

Thanks,

Barry