experimental code for SMP, does nothing exciting yet

Rev: src/acconfig.h:1.83
Rev: src/array.h:1.32
Rev: src/configure.in:1.508
Rev: src/global.h:1.59
Rev: src/mapping.h:1.35
Rev: src/multiset.h:1.17
Rev: src/object.h:1.60
Rev: src/pike_cpulib.h:1.1
Rev: src/program.h:1.121
Rev: src/stralloc.h:1.60
Rev: src/svalue.h:1.82