Better error if non-doc passed to documentMatches
History pass
expand an oplog/limit test a little

- put more info in state comments
- add a few more assertions
- stop requiring "usesOplog &&" before some helpers
failing (with oplog) test for updating a sort key
oplog-limit: don't ignore modifiers to sort key

Previously we would ignore modifier updates to documents outside our
current buffer if they did not affect the selector but did affect the
sort key.
Merge branch 'limit-sort-overlap' into devel
disallow {sort: {$natural: 1}} in minimongo
Use polling driver for {sort: {$natural: 1}}
Credit contributors.
add semicolon
Add missing selftest 'var'
Call logout in selftests that log in.

This avoids wracking up huge numbers of login tokens for the test
user. It would be nice to have these automatically cleaned up, but this
will do for now.
Make final logout unconditional for logs-mongo tests