COMSTACK API changes: cs_stackerr, cs_addrstr.

COMSTACK method cs_stackerr removed. It is not implemented by tcpip or
unix COMSTACK, perhaps for ISO SR which was removed 7 years ago.
COMSTACK macro / method cs_addrstr now returns 'const char *'
rather than 'char *. The returned string is read-only and should not
be modified by applications. COMSTACK cs_close is now a void function
- it no longer returns int. No applications check for the value and
the implementations has always returned 0.