DMStag: DMStagSetUniformCoordinatesExplicit(): linearly extrapolate to ghost regions
Set local coordinates instead of global ones, over the entire ghost region.
This provides more intuitive behavior, since users might expect coordinates in the ghost regions. For the periodic case, these coordinates have real meaning, if one assumes a periodicity given by the bounds provided to DMStagSetUniformCoordinatesXXX().
There is a small performance penalty from setting coordinates in the ghost regions.
Edited by Patrick Sanan