CommitLog tool

I wrote this for 0.7.6-2 because I had a need to see what log segment headers were preventing logs from flushing.

I've not had a chance to look at it in 0.8 yet. We dont not has header files anymore, so I could turn this into a function on the StorageServiceMBean.

For my use case i pulled the log headers off a server that had gone into a spin after it filled the commit log volume. nodetool was not running so these was the best solution for me.

Posting here to see if there is any interest or need. I think the best approach may be to add a function to the StorageService MBean to find out which CF's are dirty in the active log segments.