Updated comments.
Added files and test for ZoltanGridMigrator.
Added files and test for ZoltanGridMigrator.
Check for more errors.

* Wrapped some zoltan calls in ZOLTAN_SAFE_CALL.
* Added EQULLE_DEBUG define and turned on more Zoltan-debugging and
sanity checking when it is defined.
Added declarations and stub definitions for ZoltanGridMigrator.
Started working on the SubGrid-construction.
More work on the SubGridBuilder

* Ghost cells are now extracted.
* Cell-volumes and Cell-centroids are now migrated.
Added SubGridBuilder::extractNeighborFaces