Fixed calls to check_threads_etc in many places where we wait a while and can be interrupted by signals. Rev: src/backend.cmod:1.23 Rev: src/builtin_functions.c:1.420 Rev: src/dlopen.c:1.29 Rev: src/modules/CommonLog/clf.c:1.7 Rev: src/modules/Image/font.c:1.70 Rev: src/modules/Pipe/pipe.c:1.47 Rev: src/modules/files/efuns.c:1.110 Rev: src/modules/files/file.c:1.232 Rev: src/modules/files/socket.c:1.59 Rev: src/modules/files/udp.c:1.29 Rev: src/modules/system/system.c:1.120 Rev: src/object.c:1.197 Rev: src/signal_handler.c:1.216 Rev: src/threads.c:1.178