Editorial: fix typo 'an shared state' -> 'a shared state'
[dcl.ref] Fix "specificer" typo

Reported by Stephan T. Lavavej. Fixes #227.
[re.traits] Add whitespace in getloc()const
Merge pull request #229 from robdesbois/master

[futures.state] Fix typo

Reported by Rob Desbois
Editorial fix - additional instances of 'an shared state'
Merge pull request #230 from robdesbois/master

[futures.unique_future] [futures.shared_future] More typos

Reported by Rob Desbois.