Relation forks & FSM rewrite patches

Here's an updated version of the "relation forks" patch, and an
incremental FSM rewrite patch on top of that. The relation forks patch
is ready for review. The FSM implementation is more work-in-progress
still, but I'd like to get some review on that as well, with the goal of
doing more performance testing and committing it after the commit fest.

The one part that I'm not totally satisfied in the relation forks patch
is the smgrcreate() function. The question problem is: which piece of
code decides which forks to create for a relation, and when to create
them? I settled on the concept that all forks that a relation will need
are created at once, in one smgrcreate() call. There's no function to
create additional forks later on. Likewise, there's no function to
unlink individual forks, you have to unlink the whole relation.

Currently, heap_create() decides which forks to create. That's fine at
the moment, but will become problematic in the future, as it's
indexam-specific which forks an index requires. That decision should
really be done in the indexam. One possibility would be to only create
the main fork in heap_create(), and let indexam create any additional
forks it needs in ambuild function.

--
   Heikki Linnakangas
   EnterpriseDB   http://www.enterprisedb.com