Merge 2.10.x into master

After the merge, the test/run/t7733 started to fail on Jenkins.
I tried to reproduce it locally but I couldn't so I think it's
system dependent failure. Per @retronym's suggestion I moved it to pending
to not block the whole merge.

Conflicts:
	bincompat-backward.whitelist.conf
	bincompat-forward.whitelist.conf
	src/compiler/scala/tools/nsc/symtab/classfile/ClassfileParser.scala
	src/compiler/scala/tools/nsc/typechecker/ContextErrors.scala
	src/compiler/scala/tools/nsc/typechecker/Macros.scala
	src/compiler/scala/tools/nsc/typechecker/Namers.scala
	src/compiler/scala/tools/nsc/typechecker/NamesDefaults.scala
	src/compiler/scala/tools/nsc/typechecker/RefChecks.scala
	src/compiler/scala/tools/nsc/util/MsilClassPath.scala
	src/compiler/scala/tools/reflect/ToolBoxFactory.scala
	src/reflect/scala/reflect/internal/ClassfileConstants.scala
	src/reflect/scala/reflect/internal/Importers.scala
	src/reflect/scala/reflect/internal/Trees.scala
	src/reflect/scala/reflect/runtime/JavaMirrors.scala
	test/files/run/macro-duplicate/Impls_Macros_1.scala
	test/files/run/t6392b.check
	test/files/run/t7331c.check

Review by @retronym