…hings

Also, tweak the test for ignored type aliases such that replacing the type alias
by a newtype struct leads to a well-formed type definition, and errors when used
the way the type alias is used.

First of all, the lint is specific for type aliases.  Second, it turns out the
bounds are not entirely ignored but actually used when accessing associated
types.  So change the wording of the lint, and adapt its name to reality.

The lint has never been on stable or beta, so renaming is safe.

…hout "as", suggest to use the "as" form instead.

This is necessary to get rid of the type bound, and hence silence the warning.