Work around the 0-sized content item in Qt <= 5.2.

This causes an empty preview, since our shader effect source follows the
size of the content item. This is fixed in Qt 5.3, where the content item
has a properly updating size.
Fix setting arguments when invoking non-slot methods.
fix initialization order warning
make sure to include graphviz/types.h after QString to avoid possible
conflicting declarations of string.h stuff, like memcmp() and strcmp()
Merge branch '2.1'

Conflicts:
	core/tools/objectinspector/methodsextension.cpp