Minor changes and bugfixes
    
    - scl_prefix now accepts a parameter to improve
      inter-collection dependencies (#1028953)
    - modified the behavior of debuginfo generation process
    - changed command description in scl man pages
    - moved macros.scl to %{_rpmconfigdir}/macros.d directory
    - added conditional dependencies for main metapackage
    - scl_vendor macro gets automatically written into the
      macros.{scl}-config file