Support old and new Magick loader class names
Support old and new Magick loader class names

See jcupitt/libvips@99b4bcb

philip8728/sharp,digital-flowers/sharp-win32,dtest/sharp,dtest/sharp,leiyangyou/sharp,mdimitrov/sharp,mcanthony/sharp,brandonaaron/sharp,mcanthony/sharp,mcanthony/sharp,papandreou/sharp,cmtt/sharp,mdimitrov/sharp,papandreou/sharp,leiyangyou/sharp,pporada-gl/sharp,leiyangyou/sharp,cmtt/sharp,chrisriley/sharp,dtest/sharp,pporada-gl/sharp,philip8728/sharp,digital-flowers/sharp-win32,leiyangyou/sharp,lovell/sharp,lovell/sharp,lovell/sharp,mhirsch/sharp,pporada-gl/sharp,pporada-gl/sharp,lovell/sharp,brandonaaron/sharp,lovell/sharp,mdimitrov/sharp,brandonaaron/sharp,chrisriley/sharp,papandreou/sharp,philip8728/sharp,digital-flowers/sharp-win32,mhirsch/sharp,mdimitrov/sharp,philip8728/sharp,digital-flowers/sharp-win32,cmtt/sharp,digital-flowers/sharp-win32,mdimitrov/sharp,dtest/sharp,chrisriley/sharp,mcanthony/sharp,chrisriley/sharp,papandreou/sharp,cmtt/sharp,digital-flowers/sharp-win32,leiyangyou/sharp,digital-flowers/sharp-win32,mhirsch/sharp,brandonaaron/sharp,mcanthony/sharp,papandreou/sharp,brandonaaron/sharp,chrisriley/sharp,pporada-gl/sharp,mhirsch/sharp,dtest/sharp,lovell/sharp,philip8728/sharp