ValidationQuery for Derby is fixed

ValidationQuery for Derby seems to be wrong. When we try to start
the app with Derby, it was giving SqlExceptions. After we changed
the ValidationQuery to correct version, it successfully passed.
Please check http://bit.ly/1d5rTxm as reference of the fix.
Update LabelTag.java

Matt,

I noticed in our environment LabelTag was taking up a lot of memory, I added the doEndTag method to clear the requestContext which was what was taking up the memory in each user thread on the app server. For some reason just adding requestContext = null to the release method didn't work, I actually had to add the doEndTag method, after doing this the mem usaged dropped, I didn't notice any bugs as a result of this change.
Merge pull request #17 from schrootenb/patch-1

Update LabelTag.java to reduce memory usage.
Merge pull request #15 from lemiorhan/master

Fix ValidationQuery for Derby.