Auto-invalidate Java sources in every cycle during pipelining

[eed3si9n]

Fixes #918

This reverts #912 and re-invalidates all Java sources in every cycle during pipelining.
This also adds a minor fix and use options.pipelining (this module is pipelining) instead of isPickleJava (this module is providing pickle JAR), and adds a comment explaining why we do this.

before

sbt:sbtRoot> utilScripted/clean
sbt:sbtRoot> utilScripted/compile
sbt:sbtRoot> utilScripted/compile
[error] ${BASE}/internal/util-scripted/src/main/scala/sbt/internal/scripted/HandlersProvider.scala:11:27: not found: type ScriptConfig
[error]   def getHandlers(config: ScriptConfig): Map[Char, StatementHandler]
[error]                           ^
[error] ${BASE}/internal/util-scripted/src/main/scala/sbt/internal/scripted/ScriptedTests.scala:146:30: not found: type ScriptConfig
[error]       val scriptConfig = new ScriptConfig(label, testDirectory, log)
[error]                              ^
[error] two errors found

after

sbt:sbtRoot> utilScripted/clean
sbt:sbtRoot> utilScripted/compile
sbt:sbtRoot> utilScripted/compile
[info] compiling 9 Scala sources to /private/tmp/sbt/core-macros/target/scala-2.12/classes ...
[info] compiling 1 Java source to /private/tmp/sbt/internal/util-scripted/target/scala-2.12/classes ...
[info] [sig files written]
[info] compiling 2 Scala sources and 1 Java source to /private/tmp/sbt/internal/util-scripted/target/scala-2.12/classes ...
[info] [sig files written]