DOC: minor fix on {sc,src}_kbytes_{in,out}

These ones report total amount of bytes, not byte rates.
This fix should be backported into 1.5 which has the same error.
DOC: fix alphabetical sort of converters

For an unknown reason, these ones were not sorted.
MEDIUM: stick-table: implement lookup from a sample fetch

Currently we have stktable_fetch_key() which fetches a sample according
to an expression and returns a stick table key, but we also need a function
which does only the second half of it from a known sample. So let's cut the
function in two and introduce smp_to_stkey() to perform this lookup. The
first function was adapted to make use of it in order to avoid code
duplication.
MEDIUM: stick-table: add new converters to fetch table data

These new converters make it possible to look up any sample expression
in a table, and check whether an equivalent key exists or not, and if it
exists, to retrieve the associated data (eg: gpc0, request rate, etc...).

Till now it was only possible using tracking, but sometimes tracking is
not suited to only retrieving such counters, either because it's done too
early or because too many items need to be checked without necessarily
being tracked.

These converters all take a string on input, and then convert it again to
the table's type. This means that if an input sample is of type IPv4 and
the table is of type IP, it will first be converted to a string, then back
to an IP address. This is a limitation of the current design which does not
allow converters to declare that "any" type is supported on input. Since
strings are the only types which can be cast to any other one, this method
always works.

The following converters were added :

  in_table, table_bytes_in_rate, table_bytes_out_rate, table_conn_cnt,
  table_conn_cur, table_conn_rate, table_gpc0, table_gpc0_rate,
  table_http_err_cnt, table_http_err_rate, table_http_req_cnt,
  table_http_req_rate, table_kbytes_in, table_kbytes_out,
  table_server_id, table_sess_cnt, table_sess_rate, table_trackers.
MINOR: samples: add two converters for the date format

This patch adds two converters :

   ltime(<format>[,<offset>])
   utime(<format>[,<offset>])

Both use strftime() to emit the output string from an input date. ltime()
provides local time, while utime() provides the UTC time.
BUG/MAJOR: http: correctly rewind the request body after start of forwarding

Daniel Dubovik reported an interesting bug showing that the request body
processing was still not 100% fixed. If a POST request contained short
enough data to be forwarded at once before trying to establish the
connection to the server, we had no way to correctly rewind the body.

The first visible case is that balancing on a header does not always work
on such POST requests since the header cannot be found. But there are even
nastier implications which are that http-send-name-header would apply to
the wrong location and possibly even affect part of the request's body
due to an incorrect rewinding.

There are two options to fix the problem :
  - first one is to force the HTTP_MSG_F_WAIT_CONN flag on all hash-based
    balancing algorithms and http-send-name-header, but there's always a
    risk that any new algorithm forgets to set it ;

  - the second option is to account for the amount of skipped data before
    the connection establishes so that we always know the position of the
    request's body relative to the buffer's origin.

The second option is much more reliable and fits very well in the spirit
of the past changes to fix forwarding. Indeed, at the moment we have
msg->sov which points to the start of the body before headers are forwarded
and which equals zero afterwards (so it still points to the start of the
body before forwarding data). A minor change consists in always making it
point to the start of the body even after data have been forwarded. It means
that it can get a negative value (so we need to change its type to signed)..

In order to avoid wrapping, we only do this as long as the other side of
the buffer is not connected yet.

Doing this definitely fixes the issues above for the requests. Since the
response cannot be rewound we don't need to perform any change there.

This bug was introduced/remained unfixed in 1.5-dev23 so the fix must be
backported to 1.5.