imports e.g. test_support must do so using an absolute package name
such as "import test.test_support" or "from test import test_support".
This also updates the README in Lib/test, and gets rid of the
duplicate data dirctory in Lib/test/data (replaced by
Lib/email/test/data).
Now Tim and Jack can have at it. :)
builtin_eval wasn't merging in the compiler flags from the current frame;
I suppose we never noticed this before because future division is the
first future-feature that can affect expressions (nested_scopes and
generators had only statement-level effects).