Make the test use .map extension for the Map file.

Before refactoring, algorithm was treating .xml as XML file, and everything else
as Map. Now all the Map files should have .map extension, and error is thrown
on anything except .xml and .map.

Refs #7765

Code/Mantid/Framework/DataHandling/test/GroupDetectors2Test.h

@@ -37,7 +37,7 @@ class GroupDetectors2Test : public CxxTest::TestSuite
   GroupDetectors2Test() :
       inputWS("groupdetectorstests_input_workspace"),
         outputBase("groupdetectorstests_output_basename"),
-        inputFile(Poco::Path::current()+"GroupDetectors2Test_mapfile_example")
+        inputFile(Poco::Path::current()+"GroupDetectors2Test_mapfile_example.map")
   {
     // This is needed to load in the plugin algorithms (specifically Divide, which is a Child Algorithm of GroupDetectors)
     FrameworkManager::Instance();