adapt findospray for ospray version 1.2

starting in ospray 1.2, embree is no longer packaged and you must
build it separately. This change fixes the "build vtk with
ospray's build directory" option. The "build vtk with ospray's
install directory" option appears to work as is, at least in the
case I've tested where both ospray and embree are installed
in the same place.

CMake/FindOSPRay.cmake

@@ -42,6 +42,7 @@ else()
     #find corresponding source directory
     load_cache(${OSPRAY_BUILD_DIR} READ_WITH_PREFIX OSP_
       CMAKE_HOME_DIRECTORY
+      embree_DIR
       )
     set(OSPRAY_SOURCE_DIR ${OSP_CMAKE_HOME_DIRECTORY})
 
@@ -54,7 +55,7 @@ else()
 
     set(LIB_OSPRAY_EMBREE LIB_OSPRAY_EMBREE-NOTFOUND)
     find_library(LIB_OSPRAY_EMBREE NAMES ospray_embree embree
-      PATHS ${OSPRAY_BUILD_DIR} NO_DEFAULT_PATH)
+      PATHS ${OSPRAY_BUILD_DIR} ${OSP_embree_DIR} NO_DEFAULT_PATH)
     mark_as_advanced(LIB_OSPRAY_EMBREE)
 
     set(LIB_OSPRAY_COMMON LIB_OSPRAY_COMMON-NOTFOUND)