Added build profile for Scala IDE for Eclipse Juno

* Updated tycho version to 0.16.0.
* New ``juno`` profile for building the plug-in for
  the Scala IDE for Eclipse Juno (default values are
  for building the nightly Scala IDE for Eclipse Indigo)
* Updated default scala.version to:
    * 2.10.2-SNAPSHOT when building against the Scala IDE 4.0.x nightly.
    * 2.10.1 when building against the Scala IDE 3.0.
Merge pull request #20 from scala-ide/issue/fix-pr-validator

Added build profile for Scala IDE for Eclipse Juno