Merge branch 'release/0.4.0-p1' into develop
fix #2: support session::close()/open() feature

+ limitation: open() couldn't change host/port/transport.
  open() simply close existing internal sessions by close().
+ add close() to client_transport interface. now, tcp,
  upd, unix transport support close().
Merge branch 'fix/2' into develop
issue #1: configuarable session-pool expire time and limit size

+ add session_pool::set_pool_time_limit(sec). default is 60sec
+ add session_pool::set_pool_size_limit(size). default is 0
  ( = unlimited ). Please note that
  - when pool-size reach limit, raise too_many_session_error
  - even if pool-size reach limit, existing idle sessions are not
    freed. these are freed only by expire-time
fix codestyle ( ident by tabs )
update ChangeLog and bump version
Merge branch 'release/0.4.1'