- cleanup #defines: I do not follow the rationale behind the
   odd line-wrapped defines at the beginning of the file.  If
   we have to use multiple lines, then we might as well do so
   cleanly and according to normal practice...

 - Remove a level of indirection: do not have spin_lock_foo
   use spin_lock - just explicitly call what is needed.

 - we do not need to define the spin_lock functions twice, once
   for CONFIG_PREEMPT and once for !CONFIG_PREEMPT.  Defining
   them once with the preempt macros will optimize away fine.

 - cleanup preempt.h too

 - other misc. cleanup, improved comments, reordering, etc.