Add 'pulls compare branch1 branch2' showing only the merge PR commits th...

showing only the merge PR commits that are in branch1 that are not in branch2

I'm hoping that this will make the production of update/patch release PR's trivial - I'm sure we can make it do more - this was as far as I got in my 'docs dev time' for the week :)

To describe the process I've gone through (using `origin` == my github repo, `upstream` == the docker/docker repo), and cherry picking documentation changes from master.


```
$ git fetch --all
$ git checkout -b post-1.3.0-docs-update-1 upstream/docs
$ pulls --remote upstream compare upstream/master post-1.3.0-docs-update-1
```

The output is markdown, and when pasted into a GH issue in the `docker/docker` repo, the #PR will link to the PR you want to review to find out if it applies to the current release, or needs to wait until the next release..

Start from the bottom and work up (I wonder if I should change this as the merge PR will be the reverse..)

- 528c15afeda9ef4d4b354d7aaf1be109b14d4110 #8622 : Coaxial/patch-1 Update dockerimages.md
- 5160fbb447586bedd20a58be9be26752419bc3f1 #8649 : mavenugo/master Fixed a minor docs issue in a Dockerfile Example
- 005029cbddfba813e8565ff7da4fd356b242a0c8 #8483 : duglin/TabTest Add a testcase to make sure we don't squash tabs or convert them to spaces
- 75fd1b614dfd5acd36975357b51341585f89003c #8639 : erikh/fix_escapes builder: fix escaping for ENV variables.
- 3c325f89e544415bafc23006ead0bdc21cab2f61 #8415 : LK4D4/use_logs_in_builder Use logs instead of attach for builder
- b357f76e5dfea46079ef8a06d0e23e08f14fd12f #8565 : LK4D4/remove_fixtures_copy_tests Remove fixtures copy tests
- fb5e6526d8b32801ee339dd2b328f6685cd66c0e #8561 : albers/bash-completion Fix support for --env-file in bash completion
- 04932e38afa78441e60ba6b86021a61a70e4692c #8614 : ryanrdetzel/master exec docs syntax fix
- 5a20dc67b005717a0549fe504a3b0ccf62c913c6 #8567 : LK4D4/add_log_done Add logDone for TestBuildAddSingleFileToNonExistDir
- 09ceae5c9c268f2b79954b1580c5ec1632f24d0e #8486 : duglin/Issue5701 Add failing testcase for single quotes in CMD
- 6ac9768eaf0d7f4ebe9dcf8205903f5a4cf1a518 #8569 : jfrazelle/Cleanup-errorOut-resp Cleanup: integration-cli (get rid of errorOut)
- 83761be409ff830ebcbd122428ff9209a7a17ae9 #8635 : blakery/master Cleanup: Removed unused function layerArchive
- 9b795108c7c15c531c1ef06889b0e975a822059d #8621 : zhgwenming/lxc Fix lxc driver build issue on Mac OS X
- 10f78974ca515e3b7224b8cedd1fb3faa94af641 #8588 : dqminh/remove-sslv3 remove sslv3 from server's TLS supported versions
- 6ce4f82ebe822dbc3cf945abba5f8a09ca48ea9f #8531 : SvenDowideit/move-registry-search-to-registry-api Move registry search API docs into the registry API document.
- 57263ef0d6255f7b46b91fefb3c059d01efa35d0 #8591 : fredlf/1.3release-notes Edits and additions to release notes.
- 62cb97278d1ff35a13a09cc845c64d6a417f5874 #8599 : irachex/commit_docs Fix commit api document
- cb106e74a14a37157b09459965a69c944f9c19f0 #8238 : vbatts/vbatts-daemon_timestamps daemon logging: unifying output and timestamps
- 2e35d7c905756314c12e10a50b36ecc46a70d31a #8544 : SvenDowideit/link-to-latest-b2d-installers Link directly to the 'latest' release alias
- 69e3a55560df06a23cc74ba54badf120e5271bf9 #8516 : jamtur01/sshd Minor changes to SSHd example
- 2f9ffe5b6ac1c547d1b5c228637007b05af48a3f #8232 : vbatts/vbatts-devmapper_getDeps devmapper: include dm_deps information in debug
- 0e67cf0627a60595f0aac51693f9266a893d5295 #8380 : cpuguy83/moar_names Add more names
- 4b594721c409318040d691d2dc1a58dbbab888b5 #8465 : SvenDowideit/document-device-flag-permission-options Add info on --device flag permissions ':rwm'
- f0eb1ef4e17b76cf628b1c233017cbf87963257f #8526 : vbatts/vbatts-too_many_open_files client: even cleaner use of Transport
- b3cda9fc7e9dbdc23619c84ed91ad41d931b6e27 #8566 : jfrazelle/Cleanup-fmt-%q Cleanup: integration-cli ('%s' with %q)
- 1183abc4aa98c92b69f8134f3fd83e1071d0cc52 #8549 : vieux/pkg_units add BytesSize in pkg/units
- d1aca045b3970a862f6bfb0b8106e9266b66f88c #8612 : jfrazelle/8611-ip-masq-iptables Setting iptables=false should propagate to ip-masq=false
- 40a6461d16f9fc4111e9c9a844447d0a7170ce41 #8606 : tianon/release-home Fix more missing HOME references
- c3237cc9d8356be505e29f22967aa84ea0c939d0 #8608 : crosbymichael/merge_release_v1.3.0 Merge release v1.3.0
- 3d0d2fd183cbe3b95982aaf0d0c62d29961d927f #8609 : gesellix/patch-2 fix minor docs error
------- ^^^^ un-considered candidates
- 2eb9c0bfd457665840b1bc5b80cc5a967c1ede5d #8595 : fredlf/signed-image-doco Expanded release notes

Cherry-pick the PR commit _only_, using 

```
   $  git cherry-pick -x -m 1 <the git MERGE commit ID>
```

This will squash all the commits in that PR into the one Merge commit, using the merge commit message (so you can easily go from the commit log to the PR, and in the process this will allow the `pulls compare` to work.

At any time, you can re-run `pulls compare` on your local branch (or between any branches)

so for example, after progressing with the above analysis, re-running looks like:

```
]$ pulls --remote upstream compare upstream/master post-1.3.0-docs-update-1
```

- 528c15afeda9ef4d4b354d7aaf1be109b14d4110 #8622 : Coaxial/patch-1 Update dockerimages.md
- 5160fbb447586bedd20a58be9be26752419bc3f1 #8649 : mavenugo/master Fixed a minor docs issue in a Dockerfile Example
- 005029cbddfba813e8565ff7da4fd356b242a0c8 #8483 : duglin/TabTest Add a testcase to make sure we don't squash tabs or convert them to spaces
- 75fd1b614dfd5acd36975357b51341585f89003c #8639 : erikh/fix_escapes builder: fix escaping for ENV variables.
- 3c325f89e544415bafc23006ead0bdc21cab2f61 #8415 : LK4D4/use_logs_in_builder Use logs instead of attach for builder
- b357f76e5dfea46079ef8a06d0e23e08f14fd12f #8565 : LK4D4/remove_fixtures_copy_tests Remove fixtures copy tests
- fb5e6526d8b32801ee339dd2b328f6685cd66c0e #8561 : albers/bash-completion Fix support for --env-file in bash completion
- 04932e38afa78441e60ba6b86021a61a70e4692c #8614 : ryanrdetzel/master exec docs syntax fix
- 5a20dc67b005717a0549fe504a3b0ccf62c913c6 #8567 : LK4D4/add_log_done Add logDone for TestBuildAddSingleFileToNonExistDir
- 09ceae5c9c268f2b79954b1580c5ec1632f24d0e #8486 : duglin/Issue5701 Add failing testcase for single quotes in CMD
- 6ac9768eaf0d7f4ebe9dcf8205903f5a4cf1a518 #8569 : jfrazelle/Cleanup-errorOut-resp Cleanup: integration-cli (get rid of errorOut)
- 83761be409ff830ebcbd122428ff9209a7a17ae9 #8635 : blakery/master Cleanup: Removed unused function layerArchive
- 9b795108c7c15c531c1ef06889b0e975a822059d #8621 : zhgwenming/lxc Fix lxc driver build issue on Mac OS X
- 10f78974ca515e3b7224b8cedd1fb3faa94af641 #8588 : dqminh/remove-sslv3 remove sslv3 from server's TLS supported versions
------- ^^^^ un-considered candidates
- cb106e74a14a37157b09459965a69c944f9c19f0 #8238 : vbatts/vbatts-daemon_timestamps daemon logging: unifying output and timestamps
- 2f9ffe5b6ac1c547d1b5c228637007b05af48a3f #8232 : vbatts/vbatts-devmapper_getDeps devmapper: include dm_deps information in debug
- 0e67cf0627a60595f0aac51693f9266a893d5295 #8380 : cpuguy83/moar_names Add more names
- f0eb1ef4e17b76cf628b1c233017cbf87963257f #8526 : vbatts/vbatts-too_many_open_files client: even cleaner use of Transport
- b3cda9fc7e9dbdc23619c84ed91ad41d931b6e27 #8566 : jfrazelle/Cleanup-fmt-%q Cleanup: integration-cli ('%s' with %q)
- 1183abc4aa98c92b69f8134f3fd83e1071d0cc52 #8549 : vieux/pkg_units add BytesSize in pkg/units
- d1aca045b3970a862f6bfb0b8106e9266b66f88c #8612 : jfrazelle/8611-ip-masq-iptables Setting iptables=false should propagate to ip-masq=false
- 40a6461d16f9fc4111e9c9a844447d0a7170ce41 #8606 : tianon/release-home Fix more missing HOME references
- c3237cc9d8356be505e29f22967aa84ea0c939d0 #8608 : crosbymichael/merge_release_v1.3.0 Merge release v1.3.0

The `------- ^^^^ un-considered candidates` marker has moved up to indicate the first PR you have not cherry=picked.

once you're happy, push the branch to GH, and make your PR - in this case against the docs branch.