Notify users about shell only if compile is present

This is a change in strategy.

The motivation is the need to find a good balance between:

  + informing the uninformed that would benefit from this information, &
  + not spamming the already informed

Making it dependent on "compile" being present in remainingCommands will
probably make it trigger for, for example, Maven users who are used to
running "mvn compile" and always run "sbt compile", and who therefore
are unneccesarily suffering terribly slow compile speeds by starting up
the jvm and sbt every time.

Fixes #3091

main/src/main/scala/sbt/Main.scala

@@ -572,13 +572,11 @@ object BuiltinCommands {
 
   private def isInteractive = System.console() != null
 
-  private def intendsToInvokeShell(state: State) =
-    (state.remainingCommands contains Shell) ||
-      (state.remainingCommands.lastOption exists (_ == s"$IfLast $Shell"))
+  private def intendsToInvokeCompile(state: State) = state.remainingCommands contains Keys.compile.key.label
 
   private def notifyUsersAboutShell(state: State): Unit = {
     val suppress = Project extract state getOpt Keys.suppressSbtShellNotification getOrElse false
-    if (!suppress && isInteractive && !intendsToInvokeShell(state) && !intendsToInvokeNew(state))
+    if (!suppress && isInteractive && intendsToInvokeCompile(state))
       state.log info "Executing in batch mode. For better performance use sbt's shell; hit [ENTER] to do so now"
   }