scala. vs. _root_.scala.

Here are a couple (now closed) bugs caused by the same thing:

https://lampsvn.epfl.ch/trac/scala/ticket/430
https://lampsvn.epfl.ch/trac/scala/ticket/805

They both caused otherwise valid code to fail when using a package
segment called scala. I found the second one fails if you just create
an empty directory called scala, even if it's never referenced at all.

The obvious thing to do would be to use rootScalaDot all the time
instead of scalaDot sometimes and rootScalaDot other times. But the
compiler won't build that way - here is the output.

http://paste.pocoo.org/show/115688/

If anyone can look at that output and/or apply their knowledge of the
compiler to propose a rigorous method for deciding which of the
remaining scalaDot calls should really be rootScalaDot and which
should not, I encourage you to spill this wisdom.