MODULES: lib1, main

STEP 0:
    libs: lib1, main
    dirty js modules: lib1, main
    dirty js files:   lib1/l1a, lib1/l1b, main/m, main/m.export, main
STEP 1..2:
    libs: lib1, main
    dirty js modules: lib1, main
    dirty js files:   lib1/l1a, lib1/l1b, main/m