Create a new API for calling Java toolchains.

* Create a new sbt.compiler.javac package
* Create new interfaces to control running `javac` and `javadoc` whether forked or local.
* Ensure new interfaces make use of `xsbti.Reporter`.
* Create new method on `xsbti.compiler.JavaCompiler` which takes a `xsbti.Reporter`
* Create a new mechanism to parse (more accurately) Warnings + Errors, to distinguish the two.
* Ensure older xsbti.Compiler implementations still succeed via catcing NoSuchMethodError.
* Feed new toolchain through sbt.actions.Compiler API via dirty hackery until we can break things in sbt 1.0
* Added a set of unit tests for parsing errors from Javac/Javadoc
* Added a new integration test for hidden compilerReporter key, including testing threading of javac reports.

Fixes #875, Fixes #1542,  Related #1178 could be looked into/cleaned up.

interface/src/main/java/xsbti/compile/JavaCompiler.java

@@ -2,6 +2,7 @@ package xsbti.compile;
 
 import java.io.File;
 import xsbti.Logger;
+import xsbti.Reporter;
 
 /** 
 * Interface to a Java compiler.
@@ -9,6 +10,17 @@ import xsbti.Logger;
 public interface JavaCompiler
 {
 	/** Compiles Java sources using the provided classpath, output directory, and additional options.
-	* Output should be sent to the provided logger.*/
+	 * Output should be sent to the provided logger.
+     *
+     * @deprecated 0.13.8 - Use compileWithReporter instead
+     */
 	void compile(File[] sources, File[] classpath, Output output, String[] options, Logger log);
-}
+
+    /**
+     * Compiles java sources using the provided classpath, output directory and additional options.
+     *
+     * Output should be sent to the provided logger.
+     * Failures should be passed to the provided Reporter.
+     */
+    void compileWithReporter(File[] sources, File[] classpath, Output output, String[] options, Reporter reporter, Logger log);
+}

util/log/src/main/scala/sbt/Logger.scala

@@ -104,6 +104,7 @@ object Logger {
       val position = pos
       val message = msg
       val severity = sev
+      override def toString = s"[$severity] $pos: $message"
     }
 }