thread_state -> Pike_interpreter, preparation for centralizing a bunch

of global variables..

Rev: src/global.h:1.43
Rev: src/interpret.h:1.44
Rev: src/modules/HTTPLoop/cache.c:1.10
Rev: src/modules/Java/jvm.c:1.20
Rev: src/threads.c:1.131
Rev: src/threads.h:1.94