BUG/MAJOR: stream_interface: fix occasional data transfer freezes

BUG/MAJOR: stream_interface: fix occasional data transfer freezes

Since the changes in connection management, it became necessary to re-enable
polling after a fast-forward transfer would complete.

One such issue was addressed after dev12 by commit 9f7c6a18 (BUG/MAJOR:
stream_interface: certain workloads could cause get stuck) but unfortunately,
it was incomplete as very subtle cases would occasionally remain unaddressed
when a buffer was marked with the NOEXP flag, which is used during POST
uploads. The wake up must be performed even when the flag is there, the
flag is used only to refresh the timeout.

Too many conditions need to be hit together for the situation to be
reproducible, but it systematically appears for some users.

It is particularly important to credit Sander Klein and John Rood from
Picturae ICT ( http://picturae.com/ ) for reporting this bug on the mailing
list, providing configs and countless traces showing the bug in action, and
for their patience testing litteraly tens of snapshots and versions of
supposed fixes during a full week to narrow the commit range until the bug
was really knocked down! As a side effect of their numerous tests, several
other bugs were fixed.