sean's nginx patch

It enables on the fly gzip of responses of the gzip_types listed.
The gzip_buffers is forcing the number and size of gzip buffers to allocate. It will make it the same across platforms.

Not sure it will be accepted upstream. The default is only text/html and it will cause different (probably unexpected) behaviour.

I introduced this because we found a bug that wasn't caught until production due to the different gzip types.