integrate gzip compression into mapio

[assefa]

e-mails related to this

e-mail from Daniel,

The way things stand right now, it seems that the SVG output won't work with 
the FastCGI or anything else that relies on the msIO_* functions, plus there 
is currently no way for the other places that use msIO* calls to benefit from 
the on-the-fly compression.

Are there specific problems that prevented you from adding compression to the 
mapio.c directly and use the regular msIO_fprintf() function to generate the 
SVG code? Or maybe using msIO_installHandlers()


e-mail from Frank,

I would very much like to see support in mapio for the gzip compression
so we can apply it in other context.  If you like, I could take a crack at
this based on what Assefa has already done.  If so,  assign an
appropriate bug to me.  

If Assefa does it, I would like to suggest we think a bit about what 
will drive this to make it work for WFS output for instance.

[bartvde@…]

Adding myself to the cc.

[warmerdam]

No action planned on this for the time being, but it would be a nice enhancement.