[cairo] surface information saving with cairo_save

[Thomas Hunger]

Hi
I wonder if it would make sense to save the current surface matrix of the 
gstate->source if source is a pattern whenever one does a cairo_save.

When using cairo_set_pattern the gstate->source (==pattern) is only referenced 
and not copied, but the user might expect that the pattern state itself (i.e. 
current matrix, repeat and content) is saved, too.

Saving the actual content is a performance killer, since each cairo_save and 
cairo_restore would need an entire image-data copy, but saving the surface 
matrix (and maybe repeat) should be a simple change in cairo.

just found: cairo_filter_t could also be saved.

Tom