Fix GetTickCount return type

int as a return type results in a signed/unsigned mismatch warning with MSVC (although disabled by default), and it doesn't even compile with clang-cl if the definiton from the Windows header was included before.
Added validation of invalid inner future in wrap.
rollback to not define BOOST_RESULT_OF_USE_DECLTYPE.
don't check for is_ready on all the futures when using when_wny.
don't use std::queue with MSVC 11.
Merge pull request #25 from MarcelRaad/patch-1

Fix GetTickCount return type
shared_future<R>::then() should be const.
Merge branch 'develop' of github.com:boostorg/thread into develop
Fix compilation with BOOST_USE_WINDOWS_H defined

Don't use macros defined only in Windows SDK 6.0 and later as this breaks compilation with MinGW and older MSVC.
Merge pull request #26 from Lastique/patch-3

Fix compilation with BOOST_USE_WINDOWS_H defined
Fix GCC warnings about initialization order
Merge pull request #27 from Lastique/patch-4

Fix GCC warnings about initialization order
minor changes to unwrap.
Added const to shred_future::then().