threads added

Rev: src/Makefile.src:1.9
Rev: src/backend.c:1.3
Rev: src/builtin_functions.c:1.6
Rev: src/configure.in:1.6
Rev: src/constants.c:1.3
Rev: src/error.c:1.4
Rev: src/error.h:1.3
Rev: src/interpret.c:1.5
Rev: src/interpret.h:1.3
Rev: src/machine.h.in:1.5
Rev: src/main.c:1.5
Rev: src/modules/files/configure.in:1.6
Rev: src/modules/files/efuns.c:1.3
Rev: src/modules/files/file.c:1.7
Rev: src/modules/files/file_machine.h.in:1.3
Rev: src/modules/files/socket.c:1.3
Rev: src/modules/gdbmmod/gdbmmod.c:1.2
Rev: src/modules/readlinemod/readlinemod.c:1.3
Rev: src/modules/spider/configure.in:1.4
Rev: src/modules/spider/spider.c:1.10
Rev: src/program.c:1.2
Rev: src/threads.c:1.1
Rev: src/threads.h:1.1