Merge in second phase Disk IO refactoring, separating out the store and the io logic.

Merge in second phase Disk IO refactoring, separating out the store and the io logic.

Patches applied:

 * robertc@squid-cache.org--squid/squid--disk-io--3.0--patch-15
   Merge of robertc@squid-cache.org--squid/squid--HEAD--3.0--patch-286

 * robertc@squid-cache.org--squid/squid--disk-io--3.0--patch-16
   Merge of robertc@squid-cache.org--squid/squid--HEAD--3.0--patch-287

 * robertc@squid-cache.org--squid/squid--disk-io--3.0--patch-17
   Merge of robertc@squid-cache.org--squid/squid--HEAD--3.0--patch-288

 * robertc@squid-cache.org--squid/squid--disk-io--3.0--patch-18
   Merge of robertc@squid-cache.org--squid/squid--HEAD--3.0--patch-289

 * robertc@squid-cache.org--squid/squid--disk-io--3.0--patch-19
   Merge of robertc@squid-cache.org--squid/squid--HEAD--3.0--patch-290

 * robertc@squid-cache.org--squid/squid--disk-io--3.0--patch-20
   Sync to HEAD.

 * robertc@squid-cache.org--squid/squid--disk-io--3.0--patch-21
   More OOification.

 * robertc@squid-cache.org--squid/squid--disk-io--3.0--patch-22
   Extraction of Disk IO modules.

 * robertc@squid-cache.org--squid/squid--disk-io--3.0--patch-23
   Make diskd use the IO separation facility.

 * robertc@squid-cache.org--squid/squid--disk-io--3.0--patch-24
   More diskd layering work.

 * robertc@squid-cache.org--squid/squid--disk-io--3.0--patch-25
   Rename SwapDirOption to ConfigOption.

 * robertc@squid-cache.org--squid/squid--disk-io--3.0--patch-26
   More diskd works.

 * robertc@squid-cache.org--squid/squid--disk-io--3.0--patch-27
   Move diskd's IO logic to DiskIO/DiskDaemon

 * robertc@squid-cache.org--squid/squid--disk-io--3.0--patch-28
   Finish AUFS logic separation.

 * robertc@squid-cache.org--squid/squid--disk-io--3.0--patch-29
   Add AIO Disk IO Module.

 * robertc@squid-cache.org--squid/squid--disk-io--3.0--patch-30
   Fix double-free in coss.

 * robertc@squid-cache.org--squid/squid--disk-io--3.0--patch-31
   AIO as a full IO Module.

 * robertc@squid-cache.org--squid/squid--disk-io--3.0--patch-32
   Make IO usage flexible.

 * robertc@squid-cache.org--squid/squid--disk-io--3.0--patch-33
   Make coss work with diskd.

 * robertc@squid-cache.org--squid/squid--disk-io--3.0--patch-34
   Merge of robertc@squid-cache.org--squid/squid--HEAD--3.0--patch-356

 * robertc@squid-cache.org--squid/squid--disk-io--3.0--patch-35
   Merge of robertc@squid-cache.org--squid/squid--HEAD--3.0--patch-357

 * robertc@squid-cache.org--squid/squid--disk-io--3.0--patch-36
   Merge of robertc@squid-cache.org--squid/squid--HEAD--3.0--patch-358

 * robertc@squid-cache.org--squid/squid--disk-io--3.0--patch-37
   Merge of robertc@squid-cache.org--squid/squid--HEAD--3.0--patch-359

 * robertc@squid-cache.org--squid/squid--disk-io--3.0--patch-38
   Merge of robertc@squid-cache.org--squid/squid--HEAD--3.0--patch-360

 * robertc@squid-cache.org--squid/squid--disk-io--3.0--patch-39
   Add missed files.

 * robertc@squid-cache.org--squid/squid--disk-io--3.0--patch-40
   Merge of robertc@squid-cache.org--squid/squid--HEAD--3.0--patch-361

 * robertc@squid-cache.org--squid/squid--disk-io--3.0--patch-41
   AIO stability work.

 * robertc@squid-cache.org--squid/squid--disk-io--3.0--patch-42
   Coss tidyup.

 * robertc@squid-cache.org--squid/squid--disk-io--3.0--patch-43
   Merge of robertc@squid-cache.org--squid/squid--HEAD--3.0

 * robertc@squid-cache.org--squid/squid--disk-io--3.0--patch-44
   Bugfix: coss aliasing error.

 * robertc@squid-cache.org--squid/squid--disk-io--3.0--patch-45
   Merge http_version fix.

 * robertc@squid-cache.org--squid/squid--disk-io--3.0--patch-46
   CossLog tweaks.

 * robertc@squid-cache.org--squid/squid--disk-io--3.0--patch-47
   Remove all AIO dependencies from coss.

 * robertc@squid-cache.org--squid/squid--disk-io--3.0--patch-48
   Merge from HEAD.

 * robertc@squid-cache.org--squid/squid--disk-io--3.0--patch-49
   merge from HEAD

 * robertc@squid-cache.org--squid/squid--disk-io--3.0--patch-50
   sync with MAIN

 * robertc@squid-cache.org--squid/squid--disk-io--3.0--patch-51
   merge in bugfix for auth double deletes in digest

 * robertc@squid-cache.org--squid/squid--disk-io--3.0--patch-52
   update from HEAD

 * robertc@squid-cache.org--squid/squid--disk-io--3.0--patch-53
   sync with HEAD