am c18736b1: remember device-specific releasetools extensions in target-files

Merge commit 'c18736b1a777c386dc3c5e3f878249770b5edd78' into eclair-plus-aosp

* commit 'c18736b1a777c386dc3c5e3f878249770b5edd78':
  remember device-specific releasetools extensions in target-files