Revert the change to LSM cursor reset, so they keep chunk cursors open but
reset.  While this prevents files from being closed, it should not prevent leaf
pages from being evicted.  If we see cases where it does, we will fix them in
another way, because closing and reopening cursors is too expensive for
ordinary use (e.g., when maintaining a cache of cursors).

refs #1321
Release snapshots on transaction commit, check if a new snapshot is required on the next cursor operation.
Revert some debugging.
Update some comments.
Use __asm__ consistently.
Merge pull request #1324 from wiredtiger/commit-release-snapshot

Commit release snapshot
If sweep hits a page that cannot be discarded, make sure the tree remains in a consistent state for readers.  In particular, switch the state to WT_REF_DISK for pages that are successfully discarded.

refs #1316