Someone needs to audit the usage of isspace, tolower, and friends.  There are
things like this in the code:

static int is_dev_null(const char *str)
{
	return !memcmp("/dev/null", str, 9) && isspace(str[9]);
}

Since str[9] is of type char it should not be used as a argument to
isspace directly,
but rather be cast to unsigned char:

    ... isspace((unsigned char)str[9]);

Admittedly that is ugly.  Blame K&R.  (Glibc has a partial workaround for this
kind of coding bug.  On the up side you won't get a crash, but on the down
side you can get the wrong result.)

Morten