OGR outputs fail in fastcgi mode when STORAGE is set to stream

When setting FORMATOPTION "STORAGE=stream" in an OGR outputformat, all fastcgi requests for that format will result in a 0 length response. This seems reasonable as the ```/vsistdout/``` datasource is not connected to the fastcgi msIO.

cc @rouault . is there a workaround to use msIO* functions in OGR? Would there be any reason to not switch to a memory storage if we can detect we are run in an fcgi container?