(re)introduce the subpackage functionality or debug symbols

cmssw.spec:
  - introduce debug subpackage in the DEBUG builds

coral.spec:
  - introduce debug subpackage
scram-project-build.file: fix splitting of debug symbols

  - fix the splitting of debug symbols in the .../bin/ directory
  - from David A., split and compress debug symbols in parallel
  - use the same name for all the common symbols files
Merge pull request #730 from fwyzard/IB/CMSSW_7_1_X/debug

(re)introduce the subpackage functionality for debug symbols