Merge of r4886, r4887, r4894: log variables generalization:

Merge of r4886, r4887, r4894: log variables generalization:

*) Log: $apache_bytes_sent removed.  It was renamed to $body_bytes_sent
   in nginx 0.3.10 and the old name is deprecated since then.

*) Variable $bytes_sent.  It replicates variable $bytes_sent as previously
   available in log module only.  Patch by Benjamin Grössing (with minor
   changes).

*) Variables $connection and $connection_requests.  Log module
   counterparts are removed as they aren't used often and there is no
   need to preserve them for efficiency.