Checkpoint

This is an initial go at creating a "Checkpoint" mesh format for libMesh.

These new files have extension of "cpa" and "cpr" for the ascii and binary formats respectively.

I've done some light testing (only with the ascii version so far though)... and I can successfully write and read these files with both Serial and Parallel mesh doing the right thing.  I'm sure there are bugs, but I wanted to start getting some comments on the overall design.

There are a couple of things I'm still not writing out currently: p_level and unique_id are two that I know of.  I'll fix that up soon.

I also know that I need to add this to an example... I haven't done that yet because Automake is still enough of a pain (and foreign to me) that I just work on examples in an external application instead ;-)  I'll roll up my sleeves and get it done before we're finished with this thing though ;-)