FetchV2Request round up (doneReceived, renamings)

FetchV2Request round up (doneReceived, renamings)

Make "doneReceived" a member of the fetch request. It indicates if the
"done" line has been received (so it makes sense there) and makes all
the code after the parsing depend only on the request.

Rename "shallowExcludeRefs" to "deepenNot". Those refs come in
"deepen-not" lines in the protocol, and this name makes clearer the
intention.

Change-Id: I7bec65de04930277266491d278de7c3af7d8cbe6
Signed-off-by: Ivan Frade <ifrade@google.com>