dpkg-source: factorize logic of copy of original tarballs

dpkg-source: factorize logic of copy of original tarballs

* scripts/Dpkg/Source/Package.pm (extract): Now handles copy
of original tarballs and addition of executable right to
debian/rules.
scripts/Dpkg/Source/Package/V1_0.pm (do_extract, parse_cmdline_option):
Don't copy the original tarball as it's already done by extract().
* scripts/dpkg-source.pl: New option --no-copy to not copy
the original tarballs. New option --no-check to not check signature
and checksum. Misc cleanup in the options handling code.