geoip: got rid of ugly casts when calling ngx_free().
geoip: got rid of ugly casts when calling ngx_free().

This is done by removing the "const" qualifier from the common return
type of handler functions returning either "const char *" or "char *".

firebase/nginx,firebase/nginx,hy0kl/nginx,hy0kl/nginx,firebase/nginx,firebase/nginx,hy0kl/nginx