Well ... the correct way to check it is:

Each time there's a new block check either:
1) The coinbase sig contains /solo.ckpool.org/
or
2) The 2nd address in the coinbase transaction is 1PKN98VN2z5gwSGZvGKS2bj8aADZBkyhkZ
 (and there are 2, and only 2, addresses in the coinbase transaction)

Then if the other (1st) coinbase address matches the user's address then they found the block here.

Though it's probably easier to simply check if the first address in the coinbase transaction is the user's address since that could only be a false positive if the same user used the same address and found a solo block somewhere else.

Checked out your code... it'll ping jackpot every 10 minutes if you happen to have more than 20BTC in your address.  Might want to consider another way to notify people if they've actually hit the block, since just checking the balance of an address is no indicator that the user found a block.