Fix forward-declarations of links to blocks that don't exist yet.
We do this by checking the final state of all links after loading the top-most controller file. The new code will allow an included file to create links to blocks that will only exist later on during the load process, and it will successfully error out when links are defined for non-existing block. Furthermore, controller_block_link() will now bail out immediately when it hits an unrecoverable linker error. With this change, the error mesaage of the linker step that failed will remain at the end of the output instead of being flushed off the screen by e.g. 100+ 'Linked x to y (chained)' lines. modified: controller/controller/controller_block.c modified: controller/controller/controller_load.c