This is the first of tree patches for i2c.  Trying to get the i2c
cleanups finshed before 2.6.x, so we (hopefully) don't have a
ever-changing i2c subsystem in 2.7.x again (which is very annonying for
driver maintainance).

Changes:

 * listify i2c-core, i.e. make it use <linux/list.h> instead of
   statically-sized arrays, removed lots of ugly code :)
 * added i2c_(get|put)_adapter, changed i2c-dev.c to use these
   functions instead maintaining is own adapter list.
 * killed the I2C_DF_DUMMY flag which had the strange semantics to
   make the i2c subsystem call driver->attach_adapter on detaches.
   Added a detach_adapter() callback instead.
 * some other minor cleanups along the way ...