Clean up a comment, don't bother clearing the key/value pair, it should
have already been done by our caller.
First set of changes to make WT_DATA_SOURCE work better (row-store is
working, but column-store still isn't).

Create a new cursor type, the data-source cursor; it has a "child" cursor
that's "owned" by the data-source layer.  This means adding a new private
field to the WT_CURSOR structure for a data-source.  Implementation is in
cursor/cur_ds.c.

Store the data-source configuration (currently only the key/value_format
strings) in the meta-data file.

Pass simplified configuration strings to the underlying data-source methods
("key_format", "value_format" and "append", so far, probably needs "overwrite"
as well).

Don't pass "owner" to the WT_DATA_SOURCE.open_cursor method, owner is
intended for some of the internal cursor types, like dump.

Some general renaming, use "uri" instead of "name" in the data-source
methods and docs.
Merge branch 'develop' into data-source
map both DB_NOTFOUND and DB_KEYEMPTY to WT_NOTFOUND.
Add support for "append", using DB.put DB_APPEND flag.

Remove unused #include files.
Add support routines to get/set the data-source key/value pair
so we do it consistently.
We have to position the cursor after append/create using the DB handle,
that's the semantic WiredTiger expects.
whitespace
Don't use "return" in a comment, it messes up the style check.
Change the data-source create method signature to take a char *[]cfg,
not a char *config, for consistency.   This should really be done at
a higher level throughout the source, but I'm just clipping it at an
easy spot for now.
Support the cursor overwrite flag in data-source cursors.
There's no way to reconfigure a cursor at run-time in the current system;
add a comment noting that if a way is added in the future, we need to add
a similar call to data-source cursors, or, disallow reconfiguration.
User-specified collators aren't supported for data-source objects,
catch the error.
Make it an error to set a key in a cursor configured for "append".
WiredTiger's recno is 8B, Berkeley DB's is 4B, check for overflow during
assignment.
Add support for compaction, salvage and verification to data-source
objects, plus cleanups from the last recno overflow commit.
Re-work error handling: don't return Berkeley DB errors (always return
system errno or WT_ERROR), use session.msg_printf() to report unexpected
failures.
Merge branch 'develop' into data-source
Clean up build script complaints.
Back out commit 06172ba931d518828c2290d943e91fd1ba8e10ab.