another batch of messenger patches

Here is another set of small (though not necessarily trivial) patches to the ceph client messenger code.

They are all the result of recent work that was aimed at making the messenger code more clearly based on independent states, in hopes of making the result a bit simpler and more reliable.

Most of these involve making what happens when a connection reset or closed get handled a bit more completely and/or consistently.

-Alex

[PATCH 1/9] libceph: encapsulate and document connect sequence [PATCH 2/9] libceph: encapsulate and document negotiation phase
Each of these moves some blocks of code into their own functions, and adds a lot of commentary about what's going on during the connect sequence.

[PATCH 3/9] libceph: close the connection's socket on reset
Resetting a connection clears all connection state, but never actually closes the socket. Now it will.

[PATCH 4/9] libceph: don't close socket in OPENING state
This removes the unnecessary call to con_close_socket() when a socket is found to be in OPENING state.

[PATCH 5/9] libceph: change TAG_CLOSE handling
[PATCH 6/9] libceph: kill fail_protocol()
These let the normal fault handling code take care of the receipt of a CLOSE tag from the peer, or of one of the other tags that can be sent to indicate a connection problem.

[PATCH 7/9] libceph: close connection on reset tag
This causes a more complete reset to occur when a RESETSESSION tag is received.

[PATCH 8/9] libceph: close connection on connect failure
This removes the unnecessary call to con_close_socket() when a socket is found to be in CLOSED state. (Probably should have been moved up next to patch 4/9, above.)

[PATCH 9/9] libceph: set CONNECTING state even earlier
This sets the state of a connection to CONNECTING earlier than it was occurring before.