Specify .bak for sed
Specify .bak for sed

Wrong about the reason for needing -e; the real reason is that on Mac,
'-i' swallowed up the next argument, so sed thought 'Makefile' was the
command, not the file to modify.

gridcf/gct,gridcf/gct,gridcf/gct,gridcf/gct,gridcf/gct,gridcf/gct