Make <~> work again under miniperl

Make <~> work again under miniperl

Commit a3342be368 localised %ENV before calling csh for glob.  But
that causes <~> to stop working.  So this commit clears out %ENV
*except* for $ENV{HOME}.

It relies on the way magic works:  Before localising the %ENV hash, it
retrieves its $ENV{HOME} element, which is a magical scalar.  It calls
get-magic to store the value in the scalar itself, localises %ENV, and
then calls set-magic on the element, to signal (deceitfully) that an assignment has just happened.  So the cached value in the magical sca-
lar is used and assigned to the env var.