Classes that only inherit a macro don't have a macro

Prior to this commit, a class that inherited a macro from another
class was considered by incremental compiler as having a macro.
Now, only classes that explicitly define a macro are considered as having
a macro. This influences decision whether to invalidate (recompile)
dependencies of a file that inherits a macro upon a whitespace change.
From now on, we don't invalidate dependencies in such case which
results in much better incremental compiler experience when macros are
being involved. Check #1142 for detailed discussion.

The change to the behavior is reflected by marking the
source-dependencies/inherited-macros test as passing.
The source-dependencies/macro test covers the case of defining the macro
directly in source file. Therefore we know that the desired behavior of
invalidating dependencies of macros is preserved.

Fixes #1142

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

@@ -29,6 +29,14 @@ object APIUtil
 	{
 		var hasMacro = false
 
+		// Don't visit inherited definitions since we consider that a class
+		// that inherits a macro does not have a macro.
+		override def visitStructure0(structure: Structure)
+		{
+			visitTypes(structure.parents)
+			visitDefinitions(structure.declared)
+		}
+
 		override def visitModifiers(m: Modifiers)
 		{
 			hasMacro ||= m.isMacro