connection_read_thread() return value

[Hallvard B Furuseth <h.b.furuseth@usit.uio.no>]

slapd/connection.c:connection_read_thread() returns:
- an int from connection_read() converted to long converted to void*,
- or a void* (NULL in the places I found) converted to long to int to
  long to void*.
Not sure what the idea is, but perhaps it should be cleaned up a bit:-)

-- 
Hallvard