Enhanced the CSA Login mode to accept a turn preference.

Enhanced the CSA Login mode to accept a turn preference.

Logging in the server with the CSA mode, users are now allowed to
specify a turn preference in an enhanced gamename string which
looks like <gamename>-<time>-<time>-<turn>. The first three
parts are a regular game definition. The last "-<turn>"
part is optional.
+ Without -<turn> (i.e. same as the previous behavior), there
  is no turn preference. A user's turn will be defined randomly.
+ <turn> is either "B" for black or "W" for white.