move to revised warning interface in the compiler

interface/src/main/java/xsbti/AnalysisCallback.java

@@ -26,5 +26,5 @@ public interface AnalysisCallback
 	public void api(File sourceFile, xsbti.api.SourceAPI source);
 	/** Provides problems discovered during compilation.  These may be reported (logged) or unreported.
 	* Unreported problems are usually unreported because reporting was not enabled via a command line switch. */
-	public void problem(Position pos, String msg, Severity severity, boolean reported);
+	public void problem(String what, Position pos, String msg, Severity severity, boolean reported);
 }

interface/src/main/java/xsbti/Problem.java

@@ -5,6 +5,7 @@ package xsbti;
 
 public interface Problem
 {
+	String category();
 	Severity severity();
 	String message();
 	Position position();

util/log/Logger.scala

@@ -79,9 +79,10 @@ object Logger
 			val sourceFile = o2m(sourceFile0)
 		}
 
-	def problem(pos: Position, msg: String, sev: Severity): Problem =
+	def problem(cat: String, pos: Position, msg: String, sev: Severity): Problem =
 		new Problem
 		{
+			val category = cat
 			val position = pos
 			val message = msg
 			val severity = sev