SERVER-6400: ExistsMatchExpression is always looking for a doc, so false is syntactic sugar in parser
SERVER-6400: mark doc loaded flag late so no one can overwrite
SERVER-6400: $ne is not its own operator anymore, $not + $eq
make test work with any server port
SERVER-6400 remove $not test no longer vaild
SERVER-6400: fix some $not parsing
SERVER-6400: $ne is $not + $eq
SERVER-6400: handle more cases where expressions interact in indexes (especially null and sparse)
SERVER-6400: in $all, correct embedded array walking
SERVER-6400: expose isAllDigits
SERVER-6400: fix for array walking
SERVER-6400: for leaf expressions, handled nested arrays