SERVER-10521 Implement v0.5 version of write commands protocol

The follow changes were made:
* 'ok's type is now the same as getlasterror's
* 'errMsg' is now 'errmsg', again, for getlasterror's compatibility
* 'ordered's default is now true; the field is optional
* 'writeConcern' is now optional (same as before, default {w:1})
* introduced an 'upserted' field with the _id of upserted documents
* 'multi' and 'upsert' are optional and default to false