Fix documentation of fetch-pack that implies that the client can disconnect after sending wants.

Specify conditions under which the client can terminate the connection
early. Previously, an unintended behavior was possible which could
confuse servers.

Based-on-patch-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Alex Neronskiy <zakmagnus@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/technical/pack-protocol.txt

@@ -179,18 +179,19 @@ and descriptions.
 
 Packfile Negotiation
 --------------------
-After reference and capabilities discovery, the client can decide
-to terminate the connection by sending a flush-pkt, telling the
-server it can now gracefully terminate (as happens with the ls-remote
-command) or it can enter the negotiation phase, where the client and
-server determine what the minimal packfile necessary for transport is.
-
-Once the client has the initial list of references that the server
-has, as well as the list of capabilities, it will begin telling the
-server what objects it wants and what objects it has, so the server
-can make a packfile that only contains the objects that the client needs.
-The client will also send a list of the capabilities it wants to be in
-effect, out of what the server said it could do with the first 'want' line.
+After reference and capabilities discovery, the client can decide to
+terminate the connection by sending a flush-pkt, telling the server it can
+now gracefully terminate, and disconnect, when it does not need any pack
+data. This can happen with the ls-remote command, and also can happen when
+the client already is up-to-date.
+
+Otherwise, it enters the negotiation phase, where the client and
+server determine what the minimal packfile necessary for transport is,
+by telling the server what objects it wants and what objects it has,
+so the server can make a packfile that only contains the objects that the
+client needs.  The client will also send a list of the capabilities it
+wants to be in effect, out of what the server said it could do with the
+first 'want' line.
 
 ----
   upload-request    =  want-list
@@ -219,8 +220,8 @@ If client is requesting a shallow clone, it will now send a 'deepen'
 line with the depth it is requesting.
 
 Once all the "want"s (and optional 'deepen') are transferred,
-clients MUST send a flush-pkt. If the client has all the references
-on the server, client flushes and disconnects.
+clients MUST send a flush-pkt, to tell the server side that it is
+done sending the list.
 
 TODO: shallow/unshallow response and document the deepen command in the ABNF.