abstract type T in type pattern Chisel.Ex[T] is unchecked since it is eliminated by erasure

[Aliaksei Chapyzhenka]

Running into warnings:

[info] Compiling 66 Scala sources to /home/drom/work/github/usb-bar/chisel/target/scala-2.11/classes...
[info] 'compiler-interface' not yet compiled for Scala 2.11.7. Compiling...
[info]   Compilation completed in 14.46 s
[warn] /home/drom/work/github/usb-bar/chisel/src/main/scala/Parameters.scala:455: abstract type T in type pattern Chisel.Ex[T] is unchecked since it is eliminated by erasure
[warn]           case e:Ex[T] => e
[warn]                  ^
[warn] /home/drom/work/github/usb-bar/chisel/src/main/scala/Parameters.scala:270: abstract type T in type pattern Chisel.Knob[T] is unchecked since it is eliminated by erasure
[warn]           case k:Knob[T] => ExVar[T](_VarKnob[T](k.name))
[warn]                  ^
[warn] /home/drom/work/github/usb-bar/chisel/src/main/scala/Parameters.scala:271: abstract type T in type pattern Chisel.Ex[T] is unchecked since it is eliminated by erasure
[warn]           case ex:Ex[T] => _bindLet[T](pname,ex)
[warn]                   ^
[warn] three warnings found

Not sure how critical, or important.