Few fixes to Introduce Variable (no new features added)

Added few tests to Introduce Variable
More strict requirements for expressions to introduce it.

examples/example-vfs/src/Main.kt

@@ -17,7 +17,8 @@ fun main(args : Array<String>) {
     // add watched directory
     FileSystem.write {
         for (arg in args) {
-            FileSystem.addWatchedDirectory(FileSystem.getFileByPath(arg))
+            val virtualFile = FileSystem.getFileByPath(arg)
+            FileSystem.addWatchedDirectory(virtualFile)
         }
     }
 

examples/example-vfs/src/RefreshQueue.kt

@@ -12,6 +12,7 @@ import java.util.Timer
 import java.util.TimerTask
 
 import org.jetbrains.jet.samples.vfs.utils.*
+import org.jetbrains.jet.samples.vfs.utils.listDifference
 
 /**
  * Singleton which creates thread for periodically checking if there are changes in
@@ -55,6 +56,7 @@ internal object RefreshQueue {
             val oldChildren = fileInfo.children
             val newChildren = file.children()
 
+
             val addedChildren = listDifference(newChildren, oldChildren)
             val deletedChildren = listDifference(oldChildren, newChildren)
             val commonChildren = listIntersection(oldChildren, newChildren)

examples/example-vfs/src/Test.kt

@@ -1,5 +1,8 @@
-fun x(x: Int = 1) {}
-/*
-val i = 1
-fun x(x: Int = i) {}
-*/
+fun a(op: (Int) -> Int) {}
+fun b() {
+    a {it}
+    a {
+      it
+    }
+    2 + 2
+}