Move NameHashing from incremental to api subproject.

It should have been there from the beginning because NameHashing is tied
to internals of the API subproject.

It was added to incremental subproject by mistake.

compile/api/src/main/scala/xsbt/api/NameHashing.scala

@@ -1,4 +1,4 @@
-package sbt.inc
+package xsbt.api
 
 import xsbti.api.SourceAPI
 import xsbti.api.Definition
@@ -6,7 +6,10 @@ import xsbti.api.DefinitionType
 import xsbti.api.ClassLike
 import xsbti.api._internalOnly_NameHash
 import xsbti.api._internalOnly_NameHashes
-import xsbt.api.Visit
+import xsbti.api.DefinitionType.ClassDef
+import xsbti.api.DefinitionType.Module
+import xsbti.api.DefinitionType.PackageModule
+import xsbti.api.DefinitionType.Trait
 
 /**
  * A class that computes hashes for each group of definitions grouped by a simple name.

compile/api/src/test/scala/xsbt/api/NameHashingSpecification.scala

@@ -1,8 +1,7 @@
-package sbt.inc
+package xsbt.api
 
 import org.junit.runner.RunWith
 import xsbti.api._
-import xsbt.api.HashAPI
 import org.specs2.mutable.Specification
 import org.specs2.runner.JUnitRunner
 

compile/inc/src/main/scala/sbt/inc/Compile.scala

@@ -154,7 +154,7 @@ private final class AnalysisCallback(internalMap: File => Option[File], external
 		if (APIUtil.isScalaSourceName(sourceFile.getName) && APIUtil.hasMacro(source)) macroSources += sourceFile
 		publicNameHashes(sourceFile) = {
 			if (nameHashing)
-				(new NameHashing).nameHashes(source)
+				(new xsbt.api.NameHashing).nameHashes(source)
 			else
 				emptyNameHashes
 		}