Commit Briefs
allow directory to be read again using offset 0
The documentation says explicitly that the offset is *either* 0 or the last offset plus count; that means that after some read a client can require *again* an offset 0 (i.e. doing a rewinding the directory.)
implement Tread against directories
To do so it was needed to modify the np_* functions so they take an explicit evbuffer.
free evp only if it was allocated
apparently, evbuffer_free doesn't like NULLs