Declare dependencies on decompressors
    
    Archive-Extract is a wrapper for many archive formats. Each format
    has multiple supported decompressors.
    
    This commit declares the dependencies on decompressors using virtual
    (dummy, empty) packages because current RPM does not support
    dijunction. Once rich dependencies become supported by RPM, they can
    be replaced by simple boolean expression.
    
    Originally, Archive-Extract did not require any decompressor. But it
    turned out, that some applications does expect it and it surprises
    users as this is in contrast to the documentation of the Perl module.
    
    See bug #1217352 for more details.