Closes#18959
Technically, this causes code that once compiled to no longer compile, but
that code probably never ran.
[breaking-change]
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Not quite sure the error message is good enough, I feel like it ought to tell you "because it inherits from non-object-safe trait Foo", so I've opened up a follow-up issue #19538
In regards to:
https://github.com/rust-lang/rust/issues/19253#issuecomment-64836729
This commit:
* Changes the #deriving code so that it generates code that utilizes fewer
reexports (in particur Option::* and Result::*), which is necessary to
remove those reexports in the future
* Changes other areas of the codebase so that fewer reexports are utilized
