Fixed a few warnings.

Rev: src/backend.c:1.55
Rev: src/compilation.h:1.19
Rev: src/dynamic_load.c:1.43
Rev: src/encode.c:1.68
Rev: src/gc.c:1.124
Rev: src/interpret.c:1.165
Rev: src/interpret.h:1.64
Rev: src/module_support.c:1.37
Rev: src/modules/Parser/parser.c:1.10
Rev: src/modules/call_out/call_out.c:1.39
Rev: src/modules/spider/xml.c:1.26
Rev: src/modules/sprintf/sprintf.c:1.73
Rev: src/opcodes.c:1.90
Rev: src/operators.c:1.100
Rev: src/pike_types.c:1.136
Rev: src/program.c:1.263