Standardize worker preamble

The impetus here is to enable the automatic inclusion of the extlib/
directory, which is mostly a production related move. This standardizes
our preamble template to load extlib, let it be overriden from cgi-bin,
and then hook in ljlib.
(Bug #5068) Add layout credit to Lefty

Make the credit module work correctly in Lefty.
Change MEDIUMINT to INT for comments/counters

Note: this does not include the normal "upgrade" pathway, because
actually upgrading these columns is a very time-consuming operation and
not needed by almost anybody. If someone needs to expand their columns,
they can do it manually.

The reason for changing the table creation commands, though, is to
future-proof further Dreamwidth clusters, and to make it so future
installations use the wider column widths.

There are no code implications by having the clusters
widened. Dreamwidth runs with one cluster that uses MEDIUMINTs and one
that uses the INTs. The code doesn't care anymore (it used to, but that
was fixed a while ago).
Merge pull request #395 from LivredOr/5058_Lefty_Credit

(Bug #5068) Add layout credit to Lefty
(Bug 2272) Increase day page limits

The day page was limited to 200 items, this raises it to 2000 to be in
line with the month page.
(Bug 3734) Fix 'www.username...' URLs

Sometimes users type www.foo.dreamwidth.org when they meant
foo.dreamwidth.org. The old behavior was to drop them on the home page
except logged out. Now we just redirect them to where they were trying
to go. Far saner.