Closed Issue: test_runner httplistener_test.so crashes [45]

My application was crashing at exit with similar to the provided below callstack, and I when tried running the tests, they all passed but some of them crashed at the end.

OS: CentOS 6.4 x86_64
Compiler: GCC 4.8.1

```
... $ gdb test_runner
...
(gdb) r httplistener_test.so
...
Program received signal SIGSEGV, Segmentation fault.
0x00007ffeb80012f0 in ?? ()
...
(gdb) bt
#0 0x00007ffeb80012f0 in ?? ()
#1 0x0000000000406ea9 in std::_Sp_counted_base<(__gnu_cxx::_Lock_policy)2>::_M_release() ()
#2 0x00007ffff77ab0c3 in std::__shared_count<(__gnu_cxx::_Lock_policy)2>::~__shared_count() () at /devpkgs/include/c++/4.8.1/bits/shared_ptr_base.h:553
#3 0x00007ffff030e7c2 in std::__shared_ptr<pplx::scheduler_interface, (__gnu_cxx::_Lock_policy)2>::~__shared_ptr() () at /devpkgs/include/c++/4.8.1/bits/shared_ptr_base.h:810
#4 0x00007ffff030e7dc in std::shared_ptr<pplx::scheduler_interface>::~shared_ptr() () at /devpkgs/include/c++/4.8.1/bits/shared_ptr.h:93
#5 0x00007ffff03109ec in pplx::scheduler_ptr::~scheduler_ptr() () at /home/hrayr/build/casablanca/Release/include/pplx/pplxinterface.h:74
#6 0x00007ffff03114c0 in pplx::details::_TaskCollectionImpl::~_TaskCollectionImpl() () at /home/hrayr/build/casablanca/Release/include/pplx/pplx.h:138
#7 0x00007ffff0311710 in pplx::details::_Task_impl_base::~_Task_impl_base() () at /home/hrayr/build/casablanca/Release/include/pplx/pplxtasks.h:1739
#8 0x00007ffff033220e in pplx::details::_Task_impl<unsigned char>::~_Task_impl() () at /home/hrayr/build/casablanca/Release/include/pplx/pplxtasks.h:2437
#9 0x00007ffff033af55 in void __gnu_cxx::new_allocator<pplx::details::_Task_impl<unsigned char> >::destroy<pplx::details::_Task_impl<unsigned char> >(pplx::details::_Task_impl<unsigned char>*) () at /devpkgs/include/c++/4.8.1/ext/new_allocator.h:124
#10 0x00007ffff033725f in std::enable_if<std::allocator_traits<std::allocator<pplx::details::_Task_impl<unsigned char> > >::__destroy_helper<pplx::details::_Task_impl<unsigned char> >::value, void>::type std::allocator_traits<std::allocator<pplx::details::_Task_impl<unsigned char> > >::_S_destroy<pplx::details::_Task_impl<unsigned char> >(std::allocator<pplx::details::_Task_impl<unsigned char> >&, pplx::details::_Task_impl<unsigned char>*) () at /devpkgs/include/c++/4.8.1/bits/alloc_traits.h:281
#11 0x00007ffff0332768 in void std::allocator_traits<std::allocator<pplx::details::_Task_impl<unsigned char> > >::destroy<pplx::details::_Task_impl<unsigned char> >(std::allocator<pplx::details::_Task_impl<unsigned char> >&, pplx::details::_Task_impl<unsigned char>*) () at /devpkgs/include/c++/4.8.1/bits/alloc_traits.h:405
#12 0x00007ffff032a951 in std::_Sp_counted_ptr_inplace<pplx::details::_Task_impl<unsigned char>, std::allocator<pplx::details::_Task_impl<unsigned char> >, (__gnu_cxx::_Lock_policy)2>::_M_dispose() () at /devpkgs/include/c++/4.8.1/bits/shared_ptr_base.h:407
#13 0x0000000000406ea9 in std::_Sp_counted_base<(__gnu_cxx::_Lock_policy)2>::_M_release() ()
#14 0x00007ffff77ab0c3 in std::__shared_count<(__gnu_cxx::_Lock_policy)2>::~__shared_count() () at /devpkgs/include/c++/4.8.1/bits/shared_ptr_base.h:553
#15 0x00007ffff03127ca in std::__shared_ptr<pplx::details::_Task_impl<unsigned char>, (__gnu_cxx::_Lock_policy)2>::~__shared_ptr() () at /devpkgs/include/c++/4.8.1/bits/shared_ptr_base.h:810
#16 0x00007ffff0312802 in std::shared_ptr<pplx::details::_Task_impl<unsigned char> >::~shared_ptr() () at /devpkgs/include/c++/4.8.1/bits/shared_ptr.h:93
#17 0x00007ffff031281c in pplx::task<unsigned char>::~task() () at /home/hrayr/build/casablanca/Release/include/pplx/pplxtasks.h:3186
#18 0x00007ffff0312bb6 in pplx::task<void>::~task() () at /home/hrayr/build/casablanca/Release/include/pplx/pplxtasks.h:4159
#19 0x00007fffef7e2d89 in web::http::experimental::listener::http_linux_server::~http_linux_server() () at ../include/cpprest/http_linux_server.h:193
#20 0x00007fffef7e2df4 in web::http::experimental::listener::http_linux_server::~http_linux_server() () at ../include/cpprest/http_linux_server.h:194
#21 0x00007fffef810174 in std::default_delete<web::http::experimental::details::http_server>::operator()(web::http::experimental::details::http_server*) const () at /devpkgs/include/c++/4.8.1/bits/unique_ptr.h:67
#22 0x00007fffef80fa13 in std::unique_ptr<web::http::experimental::details::http_server, std::default_delete<web::http::experimental::details::http_server> >::~unique_ptr() () at /devpkgs/include/c++/4.8.1/bits/unique_ptr.h:184
#23 0x00007ffff6a78da2 in exit () from /lib64/libc.so.6
#24 0x00007ffff6a61ce4 in __libc_start_main () from /lib64/libc.so.6
#25 0x0000000000404c81 in _start ()
(gdb)
```