Check for locks on startup

When using simple or native lockType and the application server is not shutdown properly (kill -9), you don't notice problems until someone tries to add or delete a document. In fact, you get errors every time Solr opens a new IndexWriter on the "locked" index. I'm aware of the unlockOnStartup option, but I'd prefer to know and act properly when there's a lock, and I think it would be better to know on startup, since Solr is not going to work properly.