update debug subpackage functionality

cmssw.spec
  - clean up

cmssw-patch.spec
  - tentatively add debug subpackage functionality
scram-project-build.file: fix usage of %{usercxxflags} and USER_CXXFLAGS
Merge pull request #793 from fwyzard/IB/CMSSW_7_1_X/debug

Fix usage of %{usercxxflags} and USER_CXXFLAGS in scram-project-build.file