Merge change If6a53aa5

* changes:
  add "EXTERNAL" as special value of LOCAL_CERTIFICATE
tree: ebbaceb7b028144ba9847166395a9c0376642622
  1. core/
  2. libs/
  3. target/
  4. tools/
  5. buildspec.mk.default
  6. cleanspec.mk
  7. envsetup.sh