Some refactoring of python packing.
More checks for standalone unit tests.
Refs #1429.
Remove tabs in comments.
Detect write-write conflicts before no-overwrite cursors decide to skip an update.

refs SERVER-16351
Merge pull request #1489 from wiredtiger/no-overwrite-conflicts

Detect write-write conflicts before no-overwrite cursors decide to skip an update
Merge pull request #1485 from wiredtiger/py-packing-cleanup

Python packing cleanup