This maintains BC for existing raters that have not yet been migrated to use
the new c1-import service.
* build-aux/Makefile.am (path_c1root): New variable.
(.PHONY): Add c1root target dependency.
(program-data-copy): Copy to `@C1_IMPORT_MAPDEST@'.
(c1root): New target.
* build-aux/m4/calcdsl.m4 (C1_IMPORT_MAPDEST): Configure depending on the
existence of the `c1-import' directory.