Set Mssql Application name in connection string

We needed to be able to set the application name in a mssql connection
string, but php doesn't current toy support it.

This can be very helpful while debugging/profiling php-mssql from the SQL
server side of things.

Without this patch all mssql connections have a hard coded application name
of 'PHP 5'.

https://bugs.php.net/bug.php?id=60124

Please let me know if you have any problems applying the patch or comments
on how we can make it better/get it added to the main codebase.

Thanks,

-Dan