silly EF_NMAP. Use characters instead: 'b' for bmap (was EF_BMAP),
't' for true bmap (was EF_MAP), 'r' for revert (was EF_MAP+EF_BMAP,
more sillness), and 'n' for nmap (was EF_NMAP). Callers changed.
(EF_NMAP): Remove.
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.
