Implement header package option while calling abipkgdiff
    
    Currently, when ABI comparison occurs between two versions
    of a sub-package, we show ABI changes for all exported
    symbols. But changes which are part of public headers
    are only to be considered as ABI changes.
    Now, by providing right sub-pacakge containing public
    headers, we will filter out false postive ABI changes
    for a package update.