Mark Exec's timeout test as Windows-only
Mark Exec's timeout test as Windows-only

Workaround for #434, that killing processes is currently implemented only
for Windows (with a P/Invoke to kernel32).

Microsoft/msbuild,jeffkl/msbuild,cdmihai/msbuild,rainersigwald/msbuild,Microsoft/msbuild,chipitsine/msbuild,AndyGerlicher/msbuild,cdmihai/msbuild,jeffkl/msbuild,mono/msbuild,Microsoft/msbuild,cdmihai/msbuild,AndyGerlicher/msbuild,mono/msbuild,sean-gilliam/msbuild,cdmihai/msbuild,jeffkl/msbuild,AndyGerlicher/msbuild,Microsoft/msbuild,chipitsine/msbuild,rainersigwald/msbuild,jeffkl/msbuild,sean-gilliam/msbuild,chipitsine/msbuild,rainersigwald/msbuild,mono/msbuild,sean-gilliam/msbuild,rainersigwald/msbuild,sean-gilliam/msbuild,chipitsine/msbuild,mono/msbuild,AndyGerlicher/msbuild