Fix a compiler warning in test/format.
Update extension API names from txn_XX to transaction_XX.
Cut release 1.6.2
Bump develop release version.
Force the release date to be updated when cutting a release.
refs #580
Generalize the cursor "overwrite" configuration to apply to insert, update and remove.  Default to true, so LSM is no longer a special case.
refs #512
whitespace
typo
If overwrite is the default, do the cheap test first, testing to see if
the cursor referenced item is valid is a more expensive test.

Fix a comment.
cursor/cur_std.c: In function ‘__cursor_runtime_config’:
cursor/cur_std.c:402: warning: unused variable ‘ret’
lsm/lsm_cursor.c: In function ‘__wt_clsm_open’:
lsm/lsm_cursor.c:1065: warning: unused variable ‘cval’
Check all of the combinations of record exist/not-exist and overwrite
on/off for the insert, remove and update methods.   Add an LSM test,
it has a different code path.
Add WT_LOG_CKPT.  Remove some test code.
Changes from mjc:  Callback returns an int.  Minor fixes.
Minor cleanup and bug fix.
Add an upgrading section on the new overwrite configuration semantics.
Typo in api description.  Add comment about stat.
Minor edit to the upgrade wording for the overwrite API change.
refs #512
typo
Merge pull request #512 from wiredtiger/overwrite

Make "overwrite" default true and apply consistently to insert, update and remove operations.
Merge branch 'develop' into fine-grained-durability