Port to version 4.1 of the KVS library: lots of option changes, we can
now specify KVS_O_CREATE in all cases, and we have a real KVS_O_TRUNCATE
flag.
Rename uri_source to be wt_source, I think it's a bit cleaner than
talking about URIs.
Upgrade to using KVS namespaces instead of imposing our own namespaces
on top of the underlying KVS store.
Merge pull request #575 from wiredtiger/memrata-txn

KVS library version 4.1 (upgrade to use the KVS name-spaces).
remove unused variable
more lint, unused variables.
Memrata says don't support KVS_O_SCAN, remove a KVS_O_RECLAIM use I
missed when upgrading to 4.1.
Add some more structure to the data-source cursor-create example.
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.
Transaction ID extension methods need a real session handle.
examples/c/ex_data_source.c:578:6: error: variable 'is_visible' set but not used
Don't increment the data handle reference count if locking the handle fails.
refs #574
Merge branch 'develop' into backup-bulk