MODULES: lib1, lib2, main

STEP 0:
    libs: lib1, lib2, main
    dirty js modules: lib1, lib2, main
    dirty js files: lib1/l1, lib2/l2, main/m, main/m.export
STEP 1..4:
    libs: lib1, lib2, main
    dirty js modules: lib1, lib2
    dirty js files: lib1/l1, lib2/l2
STEP 5:
    libs: lib1, lib2, main
    dirty js modules: lib1, main
    dirty js files: lib1/l1, main/m
STEP 6:
    libs: lib1, lib2, main
    dirty js modules: lib1, lib2
    dirty js files: lib1/l1, lib2/l2