Multifile tests supported

Example of a multifile test: you create a single file under the "quick" directory and put text of all your test files into it, prepending each file with a comment as follows:

// FILE: foo
class foo

// FILE: bar
class <!FOO!>bar<!>

compiler/tests/org/jetbrains/jet/JetLiteFixture.java

@@ -116,11 +116,16 @@ public abstract class JetLiteFixture extends UsefulTestCase {
     }
 
     protected void createAndCheckPsiFile(String name, String text) {
-        myFile = createPsiFile(name, text);
+        myFile = createCheckAndReturnPsiFile(name, text);
+    }
+
+    protected JetFile createCheckAndReturnPsiFile(String name, String text) {
+        JetFile myFile = createPsiFile(name, text);
         ensureParsed(myFile);
         assertEquals("light virtual file text mismatch", text, ((LightVirtualFile) myFile.getVirtualFile()).getContent().toString());
         assertEquals("virtual file text mismatch", text, LoadTextUtil.loadText(myFile.getVirtualFile()));
         assertEquals("doc text mismatch", text, myFile.getViewProvider().getDocument().getText());
         assertEquals("psi text mismatch", text, myFile.getText());
+        return myFile;
     }
 }