modules: updated FindMagnum.cmake.
Create also plugin test debug libraries with -d suffix.

This affects only Windows when tests are enabled.
Install plugin test libraries on Windows.

They need to be installed in order for the DLL to be found when running
the test.
Merge branch 'master' into compatibility
MSVC 2013 compatibility: aargh.

I managed to port only JpegImporter, all other plugins have either too
big or too obscure dependencies, which can't be found in ready-to-use
form for Visual Studio.

Neither FreeType nor libPNG has actually usable MSVC binary. What a
shame.