Work around some clang warnings.

Work around some clang warnings.

This fixes a bunch of warnings of the form

	command.c:126:2: warning: expression result unused [-Wunused-value]
		WRITE_STATUS_ITEM(&b, SI_MTIME, "%s\n", mtime);

when compiling with clang. This warning is bogus, because the underlying call
to para_printf() can only return failure if the max_size_handler fails, but
this handler is never called here because the size of this para_buffer is
unlimited.

Casting to void makes the warning go away.