#2786: support CarpetX in Multipole

Comment (by Roland Haas):

@Steven R. Brandt could you take a look at https://bitbucket.org/einsteintoolkit/einsteinanalysis/commits/964dfa0c4bf07ac77a22ae1cac2845c99afb104c and let Lucas and I know if the change from compile time specified READS to RequireValidData is ok? This is needed to be able to use both CarpetX and Carpet.

For best visibility of the changes you will want to let Bitbucket show whitespace differences.