SI-4594 Repl settings command

A settings command for the rest of us.

The usual command line options are used, except that boolean flags
are enabled with +flag and disabled with -flag.

```
scala> :settings +deprecation

scala> new BigInt(java.math.BigInteger.TEN) { }
<console>:8: warning: inheritance from class BigInt in package math is deprecated: This class will me made final.
              new BigInt(java.math.BigInteger.TEN) { }
                  ^
res0: BigInt = 10

scala> :settings -deprecation

scala> new BigInt(java.math.BigInteger.TEN) { }
res1: BigInt = 10
```
Multivalue "colon" options can be reset by supplying no values
after the colon.  This behavior is different from the command line.

```
scala> 1 toString
warning: there were 1 feature warning(s); re-run with -feature for details
res0: String = 1

scala> :settings -language:postfixOps

scala> 1 toString
res1: String = 1

scala> :settings
-d = .
-encoding = UTF-8
-explaintypes = false
-language = List(postfixOps)
-nowarn = false

scala> :settings -language:

scala> :settings
-d = .
-encoding = UTF-8
-explaintypes = false
-language = List()
-nowarn = false
```

1 files changed, 13 insertions, 0 deletions

diff --git a/src/partest/scala/tools/partest/ReplTest.scala b/src/partest/scala/tools/partest/ReplTest.scala
index edd1f705a4..7381b8af54 100644
--- a/src/partest/scala/tools/partest/ReplTest.scala
+++ b/src/partest/scala/tools/partest/ReplTest.scala
@@ -7,6 +7,7 @@ package scala.tools.partest
 
 import scala.tools.nsc.Settings
 import scala.tools.nsc.interpreter.ILoop
+import scala.tools.partest.nest.FileUtil
 import java.lang.reflect.{ Method => JMethod, Field => JField }
 
 /** A trait for testing repl code.  It drops the first line
@@ -29,3 +30,15 @@ abstract class ReplTest extends DirectTest {
   }
   def show() = eval() foreach println
 }
+
+abstract class SessionTest extends ReplTest with FileUtil {
+  def session: String
+  override final def code = expected filter (_.startsWith(prompt)) map (_.drop(prompt.length)) mkString "\n"
+  def expected = session.stripMargin.lines.toList
+  final def prompt = "scala> "
+  override def show() = {
+    val out = eval().toList
+    if (out.size != expected.size) Console println s"Expected ${expected.size} lines, got ${out.size}"
+    if (out != expected) Console print compareContents(expected, out, "expected", "actual")
+  }
+}