Mostly, several functions that take pointers as arguments, almost
always char * pointers, had those pointers qualified with "const".
Those that returned pointers to previously const-qualified arguments
had their return values qualified as const.  Some structure members
were qualified as const to retain that attribute from the variables
from which they were assigned.

Several unused functions removed from dispatch_tcp_test.c (left over
from when it was copied from dispatch_test.c).

Minor other ISC style cleanups.