Fix an overflow issue on the sidebar on the user page.
My recent fix to the user page resulted in the sidebar overflowing the

list of review requests when the list was shorter than the sidebar

contents.
This changes the rule for the sidebar on the user page to use a float

instead of absolute positioning. Absolute positioning is what we want

for the dashboard, due to the fact that we control the size of the

dashboard itself, but as that's not (currently?) the case on the user

page, we need let it use its natural height.

Tested the user page with no content and with enough content to cause

scrolling.
Tested the dashboard page to make sure nothing broke. It wasn't affected.