Merge 2.10.x to master

The conflicts were trivial.

I manually reverted the `[nomaster] SI-7862: MANIFEST.MF file for Scala sources` during conflict resolution in build.xml (it was a backport), rather than merging in steps with `-Sours` as I usually do.

Similarly, `cb4b8eb update typesafe.artifactory-online.com to private-repo` was a trivial backport and git handled the merge as a no-op.

Review by @adriaanm

```
% export MB=`git merge-base origin/2.10.x master`

% git log --graph --oneline $MB...origin/2.10.x
*   9f62900 Merge pull request #2983 from retronym/merge/2.10.3-to-2.10.x
|\
| *   96a70e3 Merge remote-tracking branch 'origin/2.10.3' into merge/2.10.3-to-2.10.x
| |\
|/ /
| *   e2fec6b Merge pull request #2976 from retronym/backport/7862
| |\
| | * 8e11dcb [nomaster] SI-7862: MANIFEST.MF file for Scala sources
| |/
| *   892aa93 Merge pull request #2969 from retronym/ticket/7861
| |\
| | * 7f4b44b SI-7861 Don't execute internal callbacks on the user Executor
| |/
| *   e176a10 Merge pull request #2906 from retronym/merge/2.10.x-to-2.10.3
| |\
| | *   d5ce3de Merge remote-tracking branch 'origin/2.10.x' into merge/2.10.x-to-2.10.
| | |\
| | * | f4ccefe Merge remote-tracking branch 'origin/2.10.x' into merge/2.10.x-to-2.10.
| |/ /
| * | 502b9f0 Merge pull request #2878 from JamesIry/2.10.3
| * | 682cf97 Merge branch '2.10.2' into 2.10.3
|  /
* |   f0ca5ae Merge pull request #2919 from retronym/ticket/7815
|\ \
| |/
|/|
| * 733b322 SI-7815 Dealias before deeming method type as dependent
*   43dcfd0 Merge pull request #2893 from adriaanm/backport-2880-2.10.x
|\
| * cb4b8eb update typesafe.artifactory-online.com to private-repo
*   d3c8c4b Merge pull request #2882 from adriaanm/license-cleanup-2.10.x
|\
| * bf93057 Change Scala license to unmodified 3-clause BSD.
* c711828 Merge pull request #2923 from retronym/ticket/7825
* a1796aa SI-7398 Enable test for Java 8 source parser under Java 8
* bf0f9da SI-7825 Consider DEFAULTMETHOD when refchecking concreteness

% git merge origin/2.10.x
Auto-merging src/reflect/scala/reflect/internal/Types.scala
CONFLICT (content): Merge conflict in src/reflect/scala/reflect/internal/Types.scala
Auto-merging src/reflect/scala/reflect/internal/HasFlags.scala
Auto-merging src/library/scala/concurrent/Future.scala
CONFLICT (content): Merge conflict in src/library/scala/concurrent/Future.scala
Auto-merging src/compiler/scala/tools/nsc/typechecker/RefChecks.scala
CONFLICT (content): Merge conflict in src/compiler/scala/tools/nsc/typechecker/RefChecks.scala
Auto-merging build.xml
CONFLICT (content): Merge conflict in build.xml
CONFLICT (modify/delete): bincompat-forward.whitelist.conf deleted in HEAD and modified in origin/2.10.x. Version origin/2.10.x of bincompat-forward.whitelist.conf left in tree.
CONFLICT (modify/delete): bincompat-backward.whitelist.conf deleted in HEAD and modified in origin/2.10.x. Version origin/2.10.x of bincompat-backward.whitelist.conf left in tree.
warning: inexact rename detection was skipped due to too many files.
warning: you may want to set your merge.renamelimit variable to at least 1476 and retry the command.
Automatic merge failed; fix conflicts and then commit the result.
```