This is **necessary**. you are wrong. `sbt-launch-0.11.3-2.jar` and sbt0.13.0 are incompatible.


```
$ wget http://s3.amazonaws.com/heroku-jvm-langpack-scala/sbt-launch-0.11.3-2.jar
--06:13:07--  http://s3.amazonaws.com/heroku-jvm-langpack-scala/sbt-launch-0.11.3-2.jar
           => `sbt-launch-0.11.3-2.jar'
Resolving s3.amazonaws.com... 207.171.187.117
Connecting to s3.amazonaws.com[207.171.187.117]:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 1,096,763 [application/java-archive]

100%[=====================================================================================================================================>] 1,096,763    214.13K/s    ETA 00:00

06:13:14 (183.96 KB/s) - `sbt-launch-0.11.3-2.jar' saved [1096763/1096763]

 ~/launcher-test
$ mkdir project
 ~/launcher-test
$ echo "sbt.version=0.13.0" > project/build.properties
 ~/launcher-test
$ java -jar sbt-launch-0.11.3-2.jar 
[ERROR] Terminal initialization failed; falling back to unsupported
java.lang.IncompatibleClassChangeError: Found class jline.Terminal, but interface was expected
        at jline.TerminalFactory.create(TerminalFactory.java:101)
        at jline.TerminalFactory.get(TerminalFactory.java:159)
        at sbt.ConsoleLogger$.ansiSupported(ConsoleLogger.scala:85)
        at sbt.ConsoleLogger$.<init>(ConsoleLogger.scala:79)
        at sbt.ConsoleLogger$.<clinit>(ConsoleLogger.scala)
        at sbt.GlobalLogging$.initial(GlobalLogging.scala:40)
        at sbt.StandardMain$.initialGlobalLogging(Main.scala:54)
        at sbt.StandardMain$.initialState(Main.scala:60)
        at sbt.xMain.run(Main.scala:26)
        at xsbt.boot.Launch$.run(Launch.scala:55)
        at xsbt.boot.Launch$$anonfun$explicit$1.apply(Launch.scala:45)
        at xsbt.boot.Launch$.launch(Launch.scala:69)
        at xsbt.boot.Launch$.apply(Launch.scala:16)
        at xsbt.boot.Boot$.runImpl(Boot.scala:31)
        at xsbt.boot.Boot$.main(Boot.scala:20)
        at xsbt.boot.Boot.main(Boot.scala)

java.lang.IncompatibleClassChangeError: JLine incompatibility detected.  Check that the sbt launcher is version 0.13.x or later.
        at sbt.ConsoleLogger$.ansiSupported(ConsoleLogger.scala:96)
        at sbt.ConsoleLogger$.<init>(ConsoleLogger.scala:79)
        at sbt.ConsoleLogger$.<clinit>(ConsoleLogger.scala)
        at sbt.GlobalLogging$.initial(GlobalLogging.scala:40)
        at sbt.StandardMain$.initialGlobalLogging(Main.scala:54)
        at sbt.StandardMain$.initialState(Main.scala:60)
        at sbt.xMain.run(Main.scala:26)
        at xsbt.boot.Launch$.run(Launch.scala:55)
        at xsbt.boot.Launch$$anonfun$explicit$1.apply(Launch.scala:45)
        at xsbt.boot.Launch$.launch(Launch.scala:69)
        at xsbt.boot.Launch$.apply(Launch.scala:16)
        at xsbt.boot.Boot$.runImpl(Boot.scala:31)
        at xsbt.boot.Boot$.main(Boot.scala:20)
        at xsbt.boot.Boot.main(Boot.scala)
Error during sbt execution: java.lang.IncompatibleClassChangeError: JLine incompatibility detected.  Check that the sbt launcher is version 0.13.x or later.
```