@jeffkaufman 
The SSI module uses `NGX_HTTP_SSI_BUFFERED` [1], so I wanted to make sure we did not confuse it by touching that flag. And, some other modules that need it seem to define their own flag, so I thought it would be nice to do that too for us. 
Other than that, I have no arguments either for or against, as this should work with `NGX_HTTP_SSI_BUFFERED`. Want me to remove it?

[1] http://lxr.evanmiller.org/http/source/http/modules/ngx_http_ssi_filter_module.c#L958