message: Print useful message for missing ProtoBuf Environment Variable problem.
diff: @@ -118,6 +118,8 @@ class Protobuf(Dependency):
  includes.append(os.path.join(os.getenv('PROTOBUF_INCDIR')))
  elif use_conda:
  includes.append(os.path.join(os.getenv('CONDA_PREFIX'), "Library", "Include"))
  + else:
  + print("Warning: Environment Variable PROTOBUF_INCDIR or CONDA_PREFIX is not set, which may cause protobuf including folder error.")
  self.libraries = libs
  self.include_dirs = includes
  