Thread: unlock around the calls to continuations oe deferred future executions.

[SVN r86540]
Thread: try to avoid compile error with msvc.12.

[SVN r86542]
Thread: try to avoid compile error with msvc.12 or atleast remove warning C4512.

[SVN r86543]
Thread: manage system::errc as it was an real enum class, so no implicitly convertible to an int.

[SVN r86544]
Thread: added new/old tickets tests for regression purposes.

[SVN r86545]
Thread: Added missing variadic constructor for task_shared_state.

[SVN r86548]
Thread: avoid thread ambiguity on vacpp tester.

[SVN r86568]
Thread: added test for #9303.

[SVN r86569]
Thread: Added user_scheduler (loop_executor).

[SVN r86570]
Thread: Added caller_context.hpp; Change executor by Executor template parameter in async; update the number of time the failing tests are run to catch all the compilers.

[SVN r86586]
Thread: try to fix error on mscv-12 when scoped_thread uses private dummy class with enable_if.

[SVN r86595]
Thread: Added missing include.

[SVN r86599]
Thread: add _back/_front using queue_op_status interface to sync queues and update the depending classes thread_pool and user_scheduler; Simplfy some test to isolate the errors on msvc-12.

[SVN r86616]
Thread: Adding pp variadic to asyn_func and fix some typos.

[SVN r86629]
Thread: remove BOOST_THREAD_MAX_ARGS_P1.

[SVN r86697]
Thread: try to remove warning C4520: 'boost::executor_adaptor<boost::thread_pool>' : multiple default constructors specified.

[SVN r86698]
Thread: use PP only if MSVC not defined, until I can debug it.

[SVN r86714]
Thread: improve async_func to try to solve msvc issue with executor.

[SVN r86744]
Thread: Allows to force the use of boost libraries on csbl.

[SVN r86771]
Thread: for explicit constructor for nullary_function.

[SVN r86772]