Multiple compilation processes run without parallelExecution in Global := false

[ktoso]

Moved here from: typesafehub/sbt-multi-jvm#15

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In sbt-0.13 (and sbt-multi-jvm 0.3.8), we should set parallelExecution flag to false in the Global context:

parallelExcecution in Global := false

Without this setting, it looks like multiple compilation tasks run simultaneously and it causes an exeception described as below:

java.lang.RuntimeException: Could not create directory target/classes.bak
    at scala.sys.package$.error(package.scala:27)
    at sbt.IO$.createDirectory(IO.scala:155)
    at sbt.inc.ClassfileManager$$anonfun$transactional$$anon<init>(ClassfileManager.scala:37)
    at sbt.inc.ClassfileManager$$anonfun$transactionalapply(ClassfileManager.scala:33)
    at sbt.inc.ClassfileManager$$anonfun$transactionalapply(ClassfileManager.scala:33)