connection, login, socket, sessions and more!

Hi,
  for mars support I need to add an additional structure the represent
the session with the server and another the physical connection with it.
Currently the two concept are equivalent represented by TDS_SOCKET. A
physical connection have a single session so we use the same structure.
My current patch add a TDS_SESSIONS to represent physical connection but
I'm not very fun of the name. I could rename it TDS_CONNECTION but is
actually taken. Also TDS_SOCKET reminds too much a physical connection.

So I would propose

1)
- move additional fields from TDS_CONNECTION to TDS_LOGIN and use
TDS_LOGIN for all
- add a new TDS_CONNECTION structure

2)
- rename TDS_SOCKET to TDS_SESSION
- add a new TDS_SOCKET structure

3)
- move additional fields from TDS_CONNECTION to TDS_LOGIN and use
TDS_LOGIN for all
- rename TDS_SOCKET to TDS_SESSION
- add a new TDS_SOCKET structure

1) is conservative, TDS_SOCKET is not renamed (there are a lot of places
where this name is used!) 2) change a lot of files 3) a mix but
personally I vote for it

Regards
  Frediano