仿照ibatis的风格实现Log，以及添加ConnectionChecker

git-svn-id: http://code.alibabatech.com/svn/druid/trunk@299 b9813039-fb51-4c41-a8b9-e21c2acb5095

src/main/java/com/alibaba/druid/logging/NoLoggingImpl.java

@@ -0,0 +1,29 @@
+package com.alibaba.druid.logging;
+
+public class NoLoggingImpl implements Log {
+
+    public NoLoggingImpl(Class<?> clazz){
+    }
+
+    public boolean isDebugEnabled() {
+        return false;
+    }
+
+    public void error(String s, Throwable e) {
+    }
+
+    public void error(String s) {
+    }
+
+    public void debug(String s) {
+    }
+
+    public void warn(String s) {
+    }
+
+    @Override
+    public void warn(String s, Throwable e) {
+
+    }
+
+}