message: Help Cmake find OpenNI2 include path
  When compiling with OpenNI2 flag active, CMake will not be able to find OpenNI.h due to the environment path not set in OpenCVFindOpenNI2.cmake. This PR rectifies this issue.
diff: @@ -14,7 +14,7 @@ endif()
  if(WIN32)
  if(NOT (MSVC64 OR MINGW64))
  - find_file(OPENNI2_INCLUDES "OpenNI.h" PATHS "$ENV{OPEN_NI_INSTALL_PATH}Include" DOC "OpenNI2 c++ interface header")
  + find_file(OPENNI2_INCLUDES "OpenNI.h" PATHS $ENV{OPENNI2_INCLUDE} "$ENV{OPEN_NI_INSTALL_PATH}Include" DOC "OpenNI2 c++ interface header")
  find_library(OPENNI2_LIBRARY "OpenNI2" PATHS $ENV{OPENNI2_LIB} DOC "OpenNI2 library")
  else()
  find_file(OPENNI2_INCLUDES "OpenNI.h" PATHS $ENV{OPENNI2_INCLUDE64} "$ENV{OPEN_NI_INSTALL_PATH64}Include" DOC "OpenNI2 c++ interface header")
  