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, main
STEP 1:
    libs: lib1, lib2, main
    dirty js modules: lib1, lib2
    dirty js files:   lib1/l1, lib2/l2