threads now works on NT

Rev: src/Makefile.in:1.51
Rev: src/builtin_functions.c:1.60
Rev: src/error.c:1.9
Rev: src/error.h:1.8
Rev: src/las.c:1.41
Rev: src/main.c:1.33
Rev: src/object.c:1.32
Rev: src/threads.c:1.52
Rev: src/threads.h:1.27