py, unix: Allow to compile with -Wsign-compare.

py/asmx86.c

py/bc.c

py/binary.c

py/builtinimport.c

py/compile.c

py/emitbc.c

py/lexer.c

py/map.c

py/mpz.c

py/obj.c

py/obj.h

py/objint.c

py/objlist.c

py/objstr.c

py/parse.c

py/pfenv.c

py/qstr.c

py/runtime.c

py/sequence.c

py/showbc.c