initial addition of CheckpointIO capability
Merge pull request #171 from friedmud/checkpoint

Checkpoint
Fixing error in netcdf that apparently only affects OSX 10.6.8.

See also:

http://trac.macports.org/browser/trunk/dports/science/netcdf/files/patch-daputil.c.diff?rev=112984
http://trac.macports.org/ticket/41207

Thanks Hui Zhang for finding this.
UniqueID fixes
Better fix for Snow Leopard only bug
Trying one more possible fix in daputil.c that may work for Snow Leopard.
Patch from Jed Brown fixing PetscDMLibMesh on Petsc >= 3.5.