d3 or ghost cell generator enhancement

There are times when we want to remove processor - or file - boundaries - within multiblock datasets. We need to do one of the following:

• Speed up the D3 filter. This filter freezes up (running WAY slow) when running in parallel (16 ranks), on many dozens to hundreds of blocks. Sometimes, users want to keep these blocks, so they can color by block color.
• Add the ability for the Ghost Cell Generator to work on multiple blocks.