(bzero, bcopy): Obsolete BSDisms; remove. Remove some calls without

(bzero, bcopy): Obsolete BSDisms; remove.  Remove some calls without
effect.  Replace calls by struct assignment where possible.  Replace
clear buffer, copy string to buffer by strncpy().  Use assignment to
clear when that's clearer.  Replace overlapping copy through bounce
buffer by memmove().  Replace rest by standard memset() and memcpy().
Also use sizeof() instead of literal array sizes for robustness, and
instead of symbolic array sizes for clarity.