Natural whitespace handling for SBT configuration parser AKA 'no more blankies'

The idea is to remove limitation with blank lines in sbt file.

For backward compatibility only one method is modified -  EvaluateConfigurations.splitExpressions.
Most pull request contains test and sbt files.
The father of idea is  @gkossakowski, solution was implemented by @WarsawScala members in project https://github.com/WarsawScala/sbtchallenge
1. Original ToolBoxError contains less information than we need (information about line number is missing). See [scala.tools.reflect.ToolBoxFactory](https://github.com/scala/scala/blob/2.10.x/src/compiler/scala/tools/reflect/ToolBoxFactory.scala)
```scala
 def throwIfErrors() = {
        if (frontEnd.hasErrors) {
          var msg = "reflective compilation has failed: " + EOL + EOL
          msg += frontEnd.infos map (_.msg) mkString EOL
          throw ToolBoxError(msg)
        }
      }
```
2. MessageOnlyException does not have constructor with Throwable.
3. I can print the error. Which logger should I use? `ConsoleLogger(System.err).trace(e)`?