* stapsslerr.h: New file containing NSS* error number to string mappings.
Originally from mozilla NSS documentation, also seen in other GPLv2
software.
* nsscommon.c (nssError): Print error number, and text from <stapsslerr.h>.
* stap-{client,server}-connect.c (errWarn): Standardize on nssError().
* Makefile.am (nss binaries): Also link in nsscommon.c.