does anyone have objections to update swig to 1.3.29. I've tried contacting 
  the maintainer but didn't get any reply.

As I understand it, then it's fair for you to update it.

  The reasons for the intended upgrade are:

          * lots of bugfixes
          * some applications benefit from later versions .e.g GNU Radio

Sounds fine, but the key question is what the swig folks say about
1.3.29 vs. 1.3.24.  If they declare 1.3.29 the best known version, and
don't maintain 1.3.24, then upgrading is in order.   From the website
this seems to be pretty clearly the case.

  Alternatively, I propose to create swig-devel if we need to keep the older 
  version for whatever reason.

That is generally appropriate when one wants to package unstable
releases while a stable branch is maintained.  For example, net/quagga
and net/quagga-devel.  In this case, the releases are on the same
branch and ought to be backwards compatible.

I suggest just updating to 1.3.29.

-- 
        Greg Troxel <gdt@ir.bbn.com>