Some refactorings:

- Overrides added
 - usages of push_back() replaced with emplace_back()
 - Loop variable made const-refernce
 - NULL replaced with nullptr
 - Names used in the declaration and definition unified
 - size() replaced with empty
 - Identical cases merged

include/reporters/catch_reporter_junit.cpp

@@ -223,11 +223,7 @@ namespace Catch {
                     elementName = "error";
                     break;
                 case ResultWas::ExplicitFailure:
-                    elementName = "failure";
-                    break;
                 case ResultWas::ExpressionFailed:
-                    elementName = "failure";
-                    break;
                 case ResultWas::DidntThrowException:
                     elementName = "failure";
                     break;