G_fopen_sites_new

When I want to re-open a site_list-file I only can find the function G_fopen_sites_new in my manual, unhappily this functions destroys all old contents, and doesn't append the new data if I want that.

I searched for the sources of this function to create a new version which can
append, but I could not find is in the place I expected it to be:
./src/libes/gis I have looked through some other directories, but without
any luck.

Does a function to append data to a site_list allready exist ?
and if not, where can I find the source-code for G_fopen_sites_new, so that I
can program a append-version of this function ?

thanks,
Elwin