MODULES: lib1, lib3, lib2, main

STEP 0:
    libs: lib1, lib3, lib2, main
    dirty js modules: lib1, lib2, lib3, main
    dirty js files:   lib1/l1, lib2/l2, lib3/l3, main/m, main/m.export, main
STEP 1:
    libs: lib1, lib3, lib2, main
    dirty js modules: lib1
    dirty js files:   lib1/l1
STEP 2:
    libs: lib1, lib3, lib2, main
    dirty js modules: lib3
    dirty js files:   lib3/l3