[Patch, libstdc++/64584, libstdc++/64585] Clear basic_regex after imbue and make assign exception tolerant

[Marc Glisse]

On Sat, 11 Apr 2015, Tim Shen wrote:

> I realized that std::move() on an user defined iterator may cause
> compilation error, if user explicitly deletes its move ctor/assign.

That would violate the most basic iterator requirements.

-- 
Marc Glisse