Give up trying to create enough slots for extended records, don't let
the extended records get past 3 x the number of threads.
Update checkpoint code to get and release handles, so that LSM cannot
drop tables while a checkpoint is in progress.

Refs #543
Merge pull request #565 from wiredtiger/checkpoint-get-handles

Fix a race between checkpoint and LSM discarding old files.
Convert paths for __wt_dirlist to be relative to the connection home, as we do for other OS file operations.  Don't store the connection home in conn->log_path.
Initialize some variables in case the log archive thread exits before successfully calling __wt_dirlist.
lint: fix a few warnings from running s_all.
Add a new extension function __wt_ext_config_strget that returns the
configuration value from a single string instead of an array.

Change memrata code to use the new interface.
The config-scan docs were mixed up, fix them.
lint
Memory leak, found by inspetion -- free the returned value from
metadata_read.
whitespace
Make data-sources responsible for their own metadata entries.
Add standard metadata functions to the extension API.
Rename metadata_read to be metadata_search to follow the other
operation naming (insert, update, remove).
update
lint
Add examples to the WiredTiger extension methods for accessing the
metadata.
Clean up strings.  Add slot_release_lsn to fix bug when changing files.
Have hot backup retry on EBUSY in test/format.

Fixes issue #566
Merge pull request #567 from wiredtiger/metadata-move

Have data sources manage their own metadata.
Make the "source" key to WT_SESSION::create undocumented.  There are problems associated with using it from application (e.g., rename becomes ambiguous), and we don't have a real world use case yet.