poolmanager,pool: Fix precision underflow in WASS

Fixes a problem in which a large number of writers on a pool (such as what you
would see on a tape read pool) would cause the scale of a double to underflow,
causing the weigthed acailable space to become zero.  If all pools have such
high load, no pool would be availble for selection and pool manager would
report that no pool is available for staging.

The fix uses the fact that only the relative weighted available space is
relevant. Since the weighted space is calculated by dividing unweighted space
with two to the power of the load, we can subtract a constant from the load of
all pools and maintain the relative available space of each pool. The patch
first finds the lowest load of all non-full pools in the selection and
subtracts that from the load of all pools, thus normalizing the calculation.

Other pools may have even high load, still causing the precision of a double to
be insufficient, however the likelihood of selection such a pool is virtuallt
zero anyway, so this barely affects the write distribution. The normalization
does however ensure that at least one pool does not underflow (assuming
non-full pools exist at all) and thus that a pool can be selected.

Target: 2.6
Ticket: http://rt.dcache.org/Ticket/Display.html?id=7993
Require-notes: yes
Require-book: no
Merge pull request #500 from gbehrmann/fix/2.6/rb6914

poolmanager,pool: Fix precision underflow in WASS
[maven-release-plugin] prepare release 2.6.25
[maven-release-plugin] prepare for next development iteration
poolmanager: Fix infinite loop in lru partition type

Target: trunk
Require-notes: yes
Require-book: no
Request: 2.9
Request: 2.8
Request: 2.7
Request: 2.6
Acked-by: Paul Millar <paul.millar@desy.de>
Patch: http://rb.dcache.org/r/6938/
(cherry picked from commit 6750fd426d7e60da7332453a28bfbc88d228274e)
pool: Report correct client IP to billing for passive FTP transfers

The pool incorrectly reported the FTP proxy address of the FTP door
even when a direct connection between the client and the pool was
established.

Target: trunk
Request: 2.9
Request: 2.8
Request: 2.7
Request: 2.6
Require-notes: yes
Require-book: no
Acked-by: Paul Millar <paul.millar@desy.de>
Patch: http://rb.dcache.org/r/6940/
(cherry picked from commit 7e6e2ef7a8ad506293fc440cc1354eeed9c2607a)
Merge pull request #515 from gbehrmann/fix/2.6/rb6940

pool: Report correct client IP to billing for passive FTP transfers
Merge pull request #510 from gbehrmann/fix/2.6/rb6938

poolmanager: Fix infinite loop in lru partition type
Merge remote-tracking branch 'upstream/2.6' into 2.6-backport-proxy-io