Update server control API with jackctl_server_open and jackctl_server_close (see http://trac.jackaudio.org/ticket/219 for rationale).  Update drivers to support Start/Stop of slave drivers.  Update dbus to use new jackctl_server_* functions.  Freewheel driver is no longer an implicit slave of the master audio driver.  Haven't tested freewheeling, and didn't update Solaris OSS driver.  Tested slave addition by adding loopback driver, but don't have a slave driver in this branch on Linux platform to test with.