Add C++11 compiler support detection feature

This is currently copied from http://quickgit.kde.org/index.php?p=scratch%2Fdakon%2Fcmake-cxx11.git
but there is a chance that in future it will be merged into CMake proper.

cmake/Modules/CheckCXX11Features/cxx11-test-initializer_list.cpp

@@ -0,0 +1,27 @@
+#include <vector>
+
+class seq {
+public:
+    seq(std::initializer_list<int> list);
+
+    int length() const;
+private:
+    std::vector<int> m_v;
+};
+
+seq::seq(std::initializer_list<int> list)
+    : m_v(list)
+{
+}
+
+int seq::length() const
+{
+    return m_v.size();
+}
+
+int main(void)
+{
+    seq a = {18, 20, 2, 0, 4, 7};
+
+    return (a.length() == 6) ? 0 : 1;
+}