message: Add check VS version in cmake.
diff: @@ -184,6 +184,15 @@ if(UNIX)
  include(Coveralls)
  coveralls_turn_on_coverage()
  endif()
  +else(UNIX)
  + if(NOT "${CMAKE_CXX_COMPILER_ID}" STREQUAL "MSVC")
  + message(FATAL_ERROR "RINGMesh on Windows requires Microsoft Visual C++")
  + endif()
  + # 1800 corresponds to VS 12 2013.
  + # See https://en.wikipedia.org/wiki/Microsoft_Visual_C%2B%2B for VS version numbers.
  + if(MSVC_VERSION LESS 1800)
  + message(FATAL_ERROR "RINGMesh requires Visual Studio greater or equal to VS 12 2013 WIN64")
  + endif(MSVC_VERSION LESS 1800)
  endif(UNIX)
  if(CMAKE_GENERATOR STREQUAL "Unix Makefiles")
  