-- (see msDeps)
let all_home_mods = [ms_mod_name s
| s <- mod_graph, not (isBootSummary s)]
-#ifdef DEBUG
bad_boot_mods = [s | s <- mod_graph, isBootSummary s,
not (ms_mod_name s `elem` all_home_mods)]
-#endif
ASSERT( null bad_boot_mods ) return ()
-- mg2_with_srcimps drops the hi-boot nodes, returning a