depends: Add a package for qt4.6. Linux uses it by default.

We're not ready to switch to a static qt5 for Linux yet due to missing plugin
support. This adds a recipe for building a shared qt4 that we build and link
against, but don't distribute.

make USE_LINUX_STATIC_QT5=1 can be used to build static qt5 as before.

depends/patches/qt46/stlfix.patch

@@ -0,0 +1,10 @@
+--- old/config.tests/unix/stl/stltest.cpp	2011-06-23 03:45:23.000000000 -0400
++++ new/config.tests/unix/stl/stltest.cpp	2014-08-28 00:54:04.154837604 -0400
+@@ -49,6 +49,7 @@
+ #include <vector>
+ #include <algorithm>
+ #include <iostream>
++#include <cstddef>
+ 
+ // something mean to see if the compiler and C++ standard lib are good enough
+ template<class K, class T>