Allow CarpetX to implement Driver.

[Steven R. Brandt]

Several problems exist with respect to making CarpetX implement Driver.

(1) It has a grid function named regrid_error that PUGH and Carpet do not.

(2) Carpet and PUGH have periodic_x…z defaulting to true instead of false.

(3) CarpetX does not have a parameter named periodic.

[Steven R. Brandt]

Pull request for the flesh: https://bitbucket.org/cactuscode/cactus/pull-requests/163

for PUGH: https://bitbucket.org/cactuscode/cactuspugh/pull-requests/4

for Carpet: https://bitbucket.org/eschnett/carpet/pull-requests/61

for CarpetX: https://github.com/EinsteinToolkit/CarpetX/pull/299

for Cactus Examples: https://bitbucket.org/cactuscode/cactusexamples/pull-requests/4

for wvuthorns_diagnostics: https://bitbucket.org/zach_etienne/wvuthorns_diagnostics/pull-requests/15