Simple connection failover support

Hi,

Here are two patches that add simple failover support to the jdbc driver.

Patch 1 converts all references to pair of host+port variables to single InetSocketAddress
Patch 2 rewrites the url parsing to support multiple host:port pairs and modifies the low level connection opening to
retryonce all listed addresses 
I also added more cases to the unit tests to verify that I did not break any functionality.

* The connection url and connection parameters stay backwards compatible
* If there are commas in the hostname part of the url the new code will use them to split the addresses and keep them
inthe defined priority order 
* If there is any IOException or login failure during the connection phase the code will try another listed address
* I tried to keep the code still Java 1.4 compatible

-Mikko