For example, when CPACK_<GEN>_COMPONENT_INSTALL and
CPACK_MONOLITHIC_INSTALL are both set. Previously, this
combination of variable settings produced an error without
any explanation. Now, in this case CPACK_MONOLITHIC_INSTALL wins
without trouble.
This is useful for when e.g. CPACK_ARCHIVE_COMPONENT_INSTALL is
globally on and one wants MONOLITHIC install for STGZ (but not
other generators). The same behavior may be obtained by re-setting
CPACK_ARCHIVE_COMPONENT_INSTALL to 0 but in any case the
'both set' case should have been handled without error.