add version to category/package
    @cp - name of package in format category/name
    @installed - boolean value, if False, function returns cpv
    for latest available package

def _get_cpv(cp, installed=True):
    '''
    add version to category/package
    @cp - name of package in format category/name
    @installed - boolean value, if False, function returns cpv
    for latest available package
    '''
    if installed:
        return _get_portage().db[portage.root]['vartree'].dep_bestmatch(cp)
    else:
        return _porttree().dep_bestmatch(cp)