Discard installed docs
    
    The spec makes those files to install directly from the source
    directory, and not from the installed one.
    
    error: Installed (but unpackaged) file(s) found:
       /usr/share/doc/zbar-0.10/COPYING
       /usr/share/doc/zbar-0.10/HACKING
       /usr/share/doc/zbar-0.10/INSTALL
       /usr/share/doc/zbar-0.10/LICENSE
       /usr/share/doc/zbar-0.10/NEWS
       /usr/share/doc/zbar-0.10/README
       /usr/share/doc/zbar-0.10/TODO
    
    Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>