Merge branch 'master' into upstream-intervals-2

# Conflicts:
#	src/main/proto/firrtl.proto
#	src/main/scala/firrtl/LoweringCompilers.scala
#	src/main/scala/firrtl/PrimOps.scala
#	src/main/scala/firrtl/annotations/Target.scala
#	src/main/scala/firrtl/passes/CheckChirrtl.scala
#	src/main/scala/firrtl/passes/Checks.scala
#	src/main/scala/firrtl/passes/InferWidths.scala
#	src/test/scala/firrtlTests/AttachSpec.scala
#	src/test/scala/firrtlTests/CheckInitializationSpec.scala
#	src/test/scala/firrtlTests/CheckSpec.scala
#	src/test/scala/firrtlTests/ChirrtlSpec.scala
#	src/test/scala/firrtlTests/ClockListTests.scala
#	src/test/scala/firrtlTests/ConstantPropagationTests.scala
#	src/test/scala/firrtlTests/ExpandWhensSpec.scala
#	src/test/scala/firrtlTests/InternalErrorSpec.scala
#	src/test/scala/firrtlTests/LowerTypesSpec.scala
#	src/test/scala/firrtlTests/ReplaceAccessesSpec.scala
#	src/test/scala/firrtlTests/UnitTests.scala
#	src/test/scala/firrtlTests/WidthSpec.scala
#	src/test/scala/firrtlTests/WiringTests.scala
#	src/test/scala/firrtlTests/ZeroWidthTests.scala
#	src/test/scala/firrtlTests/fixed/FixedTypeInferenceSpec.scala
#	src/test/scala/firrtlTests/fixed/RemoveFixedTypeSpec.scala