gog-renderer-cairo.h missing

[Chris Shoemaker]

gog-renderer-cairo.h seems to have escaped the goffice import even though
gog-renderer-cairo.c is present.

This breaks `make dist'.  I can import this file from goffice myself,
and obviously, `make dist' doesn't really care what I put there, but I
don't understand the overall integration policy well enough to know if
it's important that I commit the version that goes with the rest of
goffice or if the most recent version is fine.

What are our integration and dependency policies for in-tree libraries?

-chris