Add two next extension functions, one to return a transaction ID,
one to return if a transaction ID is visible to the current transaction.
Review/rework all of the error handling for the top-level session
functions, make sure we push any change into the underlying store.
Add two next extension functions, one to return a transaction ID,
one to return if a transaction ID is visible to the current transaction.
minor lint, cleanup the new docs.
Upgrade to KVS version 4.2.
Merge pull request #576 from wiredtiger/memrata

Another set of memrata changes, upgrade to version 4.2.