SSI patch version 11

Attached is a new version of the SSI patch with these changes:
 
- Performance is markedly better on table scans.  Fixed by this
commit:
 
http://git.postgresql.org/gitweb?p=users/kgrittn/postgres.git;a=commitdiff;h=64ca508a0e2fa9c21dc76a5d6a5f549c27f511fa
 
- A race condition which was causing an assertion failure in DBT-2
benchmarks should be fixed.  (We'll know soon.)  This should also
close some commit-time race conditions which could cause occasional
assertion failures or allow anomalies.  This is also a first step in
handling prepared transactions.  Here's the commit:
 
http://git.postgresql.org/gitweb?p=users/kgrittn/postgres.git;a=commitdiff;h=32e945986608b0ec93000b7167bfaa395d52f473
 
- Numerous small documentation adjustments for SSI.
 
The Concurrency Control chapter and the README file still need to be
tackled.  The guy who had volunteered to do that work hasn't been
responding to emails, so I'm not sure whether he's going to come
through.  :-(  As far as I can tell, all other documentation should
be done; so if you find anything which was missed, please let me
know.
 
-Kevin