msSaveImageBufferGD should use the agg palette

[assefa]

msSaveImageBufferGD shoud also be upgarded to use the palettes. This function is called by php mapscript function when using something like $image->saveimage("") (this function Writes image object to specifed filename. If filename is empty then write to stdout).

The intention for now is to simply add the pallette logic in this function. Maybe some kind of common function would be needed specially if we add the palette support on other formats beside png.

[assefa]

commited fix for png output. Test with php mapscript (r6180)

[sdlime]

Changing the component to the general C library since this is not AGG specific. The intention was to be able to support GIF and even JPEG as well. Should be doable since this is really format independent, rather a 24-bit to 8-bit conversion. I wonder, what, if anything would blow up with a 24-bit GIF definition?

Steve

[tbonfort]

all image saving code goes through a generic function now