add and use CMake modules for valgrind client requests and quadruple precision math
add test for <type_traits> to FindCXX11Features.cmake

I fogot this one yesterday...
add a cmake check for the abi::__cxa_demangle() function

this was also forgotten. sorry...
make the build system link to the "quadmath" library if it is supported

Thanks a lot to Roland Kaufmann for the support.
Merge pull request #315 from andlaus/checks_for_quadmath_and_valgrind

add and use CMake modules for valgrind client requests and quadruple precision math