BSON::Grow push methods append to array with correct keys

RUBY-676
BSON::Grow push_doc! and push_doc

RUBY-676
RUBY-699 renaming server_op_timeout option to max_timeout_ms
Merge branch '1.x-stable-ruby-676' of github.com:gjmurakami-10gen/mongo-ruby-driver into gjmurakami-10gen-1.x-stable-ruby-676
BSON::Grow#clear! clears internal state to allow reuse

RUBY-676
pre-serialized bson for DB#command

RUBY-676
batch_write_incremental / old API completed

RUBY-676
minor: fixing typo in constant comment
RUBY-690 Test that aggregate supports explain option
Don't merge in named nil opts into command selector
RUBY-669 Support aggregation out pipeline operator
Check for the existance of a key instead of checking key value
Cleaning up references to system.users and unnecessary auth test
batch_write_incremental / old API completed

RUBY-676
Extra options are merged into the selector so ensure OrderedHash
Merge branch '1.x-stable' into 1.x-stable-ruby-676
OrderedHash needed for commands with Ruby 1.8.7

RUBY-676