Merge pull request #3 from samgabriel/master

Fixes #2 memory leak due to retained reference to the lastWarning in the SQLDiagnostic

Author: milesibastos

src/main/net/sourceforge/jtds/jdbc/SQLDiagnostic.java

@@ -408,6 +408,7 @@ void addDiagnostic(int number,
      */
     void clearWarnings() {
         warnings = null;
+        lastWarning = null;
     }
 
     /**
@@ -420,6 +421,7 @@ void checkErrors() throws SQLException {
         if (exceptions != null) {
             SQLException tmp = exceptions;
             exceptions = null;
+            lastException = null;
             throw tmp;
         }
     }