Include static methods on traits in reexports.
Test case for issue #4202
auto merge of #6384 : thomaslee/rust/issue-4202, r=catamorphism

This fixes the issue described in #4202.

From what I understood of the code, when we reexport a trait in a submodule using e.g. "pub use foo::SomeTrait", we were not previously making an effort to reexport the static methods on that trait.

I'm new to the Rust code base (and the Rust language itself) so my approach may not be kosher, but this patch works by changing the encoder to include the static methods associated with traits.

I couldn't see any tests for this area of the code, so I didn't really have any examples to go by. If tests are needed, I'm happy to work through that if I can get some assistance to do so.