Convenient aliases for the SBT build

The idea here is to avoid the need for switching
between the SBT shell and Bash.

  - Add aliases for partest, scala{,c,p,doc}
  - Change working directory for these forked processes
    to the root project base directory, rather than the
    subprojects base directory. This lets us use relative
    paths to files in a more familar way.
  - Don't log the output of forked processes with the
    `[info] ` prefix, rather pass it through directly
    to stdout.

Demo:

```
> partest --terse test/files/pos/t6231.scala
[info] Packaging /Users/jason/code/scala2/build-sbt/pack/lib/scala-partest-javaagent.jar ...
[info] Done packaging.
Selected 1 tests drawn from specified tests

.

[info] Passed: Total 1, Failed 0, Errors 0, Passed 1
[success] Total time: 3 s, completed 05/02/2016 12:44:19 PM
> scala sandbox/test.scala
[info] Running scala.tools.nsc.MainGenericRunner -usejavacp sandbox/test.scala
Hello, World!
[success] Total time: 4 s, completed 05/02/2016 12:45:08 PM
> scalac sandbox/test.scala
[info] Running scala.tools.nsc.Main -usejavacp sandbox/test.scala
[success] Total time: 3 s, completed 05/02/2016 12:45:15 PM
> scala Test
[info] Running scala.tools.nsc.MainGenericRunner -usejavacp Test
Hello, World!
[success] Total time: 1 s, completed 05/02/2016 12:45:20 PM
> scala
[info] Running scala.tools.nsc.MainGenericRunner -usejavacp
Welcome to Scala 2.11.8-20160204-090931-42525ec (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_71).
Type in expressions for evaluation. Or try :help.

scala> 1.to
to   toBinaryString   toByte   toChar   toDegrees   toDouble   toFloat   toHexString   toInt   toLong   toOctalString   toRadians   toShort   toString

scala> 1.toString
res0: String = 1

scala> :quit
[success] Total time: 8 s, completed 05/02/2016 12:45:48 PM
>
```

Author: retronym

build.sbt

@@ -200,7 +200,18 @@ lazy val commonSettings = clearSourceAndResourceDirectories ++ publishSettings +
   },
   // Remove auto-generated manifest attributes
   packageOptions in Compile in packageBin := Seq.empty,
-  packageOptions in Compile in packageSrc := Seq.empty
+  packageOptions in Compile in packageSrc := Seq.empty,
+
+  // Lets us CTRL-C partest without exiting SBT entirely
+  cancelable in Global := true,
+  // When we fork subprocesses, use the base directory as the working directory.
+  // This enables `sbt> partest test/files/run/t1.scala` or `sbt> scalac sandbox/test.scala`
+  baseDirectory in Compile := (baseDirectory in ThisBuild).value,
+  baseDirectory in Test := (baseDirectory in ThisBuild).value,
+
+  // Don't log process output (e.g. of forked `compiler/runMain ...Main`), just pass it
+  // directly to stdout
+  outputStrategy in run := Some(StdoutOutput)
 )
 
 /** Extra post-processing for the published POM files. These are needed to create POMs that
@@ -418,7 +429,6 @@ lazy val repl = configureAsSubproject(project)
   .settings(
     connectInput in run := true,
     publishArtifact := false,
-    outputStrategy in run := Some(StdoutOutput),
     run <<= (run in Compile).partialInput(" -usejavacp") // Automatically add this so that `repl/run` works without additional arguments.
   )
   .dependsOn(compiler, interactive)
@@ -465,7 +475,8 @@ lazy val replJlineEmbedded = Project("repl-jline-embedded", file(".") / "target"
       val outdir = (classDirectory in Compile).value
       JarJar(inputs, outdir, config)
     }),
-    publishArtifact := false
+    publishArtifact := false,
+    connectInput in run := true
   )
   .dependsOn(replJline)
 
@@ -819,3 +830,10 @@ def generateServiceProviderResources(services: (String, String)*): Setting[_] =
   }.taskValue
 
 buildDirectory in ThisBuild := (baseDirectory in ThisBuild).value / "build-sbt"
+
+// TODO custom argument parsers for these to autocomplete compiler options and paths
+addCommandAlias("scalac",   "compiler/compile:runMain            scala.tools.nsc.Main -usejavacp")
+addCommandAlias("scala",    "repl-jline-embedded/compile:runMain scala.tools.nsc.MainGenericRunner -usejavacp")
+addCommandAlias("scaladoc", "scaladoc/compile:runMain            scala.tools.nsc.ScalaDoc -usejavacp")
+addCommandAlias("scalap",   "scalap/compile:runMain              scala.tools.scalap.Main -usejavacp")
+addCommandAlias("partest",  "test/it:testOnly --")