When there are too many tabs to fit on the tab bar, the notebook should make
each tab narrower to fit, instead of adding scroll buttons like it does now.

Reasons:
* So I can tell at a glance how many tabs there are. Right now in Epiphany, I
can't tell if I have six tabs open or sixteen. Did I close that page or not? I
don't know!
* Opera does it this way and I like it better.
* So the tabs stay where you put them. With the scrolling behaviour, a tab can
be on the left side one minute and then on the right side. By making all the
tabs fit at once, a tab will not move around.

I don't know what to do when there are lots of tabs, like 20. However, is that
really a problem? Here's why not:
* Many web sites have icons so you can tell the tabs apart.
* There should be other ways to access the tabs, like the Tabs menu.
* The user chose to open 20 tabs. They can deal with it.

If you think bug 110540 is better: I really don't like the idea of multiple
rows. Whenever a tab opens or closes, you are completely disoriented because the
rows shift around or the tabs shuffle themselves.