much improved handling of cross-dependencies

Rev: lib/master.pike.in:1.170
Rev: src/builtin_functions.c:1.408
Rev: src/compilation.h:1.25
Rev: src/encode.c:1.130
Rev: src/global.h:1.65
Rev: src/interpret.c:1.250
Rev: src/interpret_functions.h:1.97
Rev: src/las.c:1.271
Rev: src/object.c:1.186
Rev: src/pike_types.c:1.182
Rev: src/program.c:1.381
Rev: src/program.h:1.145
Rev: src/threads.c:1.169