Treat require ::foo::bar; the same as foo::bar;

Treat require ::foo::bar; the same as  foo::bar;

[ This is cherry-picked from a branch Nicholas wrote 4 years ago, but
which was never merged. In the meantime it was agreed that 'require
::foo' should die instead of doing 'require foo'; but I've pulled it in
anyway as an interim commit, to make later cherry-picks easier. The die
will come in a later commit.
]