osd: useful debugging for when we drop requests

Signed-off-by: Sage Weil <sage@inktank.com>
Reviewed-by: Samuel Just <sam.just@inktank.com>
osd: include osdmap epoch in osd_op message operator<<

Signed-off-by: Sage Weil <sage@inktank.com>
Reviewed-by: Samuel Just <sam.just@inktank.com>
osd: add 'osd debug op order' to track and assert order of client ops

Keep a big fat slow map in memory to ensure that client ops are applied to
objects in the order the clien sent them.  This will make it easier to
catch ordering bugs due to requeuing as soon as they happen, when the logs
are easier to wade through, and not later when the client notices something
is awry.

Signed-off-by: Sage Weil <sage@inktank.com>
Reviewed-by: Samuel Just <sam.just@inktank.com>