Thanks for your help Rex and Panu.
I've updated the package, the updated .spec file is at
http://vpv.fedorapeople.org/packages/python-pymtp.spec
I decided to depend on the libmtp soname, because a libmtp soname bump
will probably lead to pymtp being broken. I used the following "trick",
once recommended to me by Ville Skyttä:
%global libmtp libmtp.so.8
%ifarch x86_64 ppc64 ia64 sparc64 s390x
%global mark64 ()(64bit)
%endif
Requires: %{libmtp}%{?mark64}
--
Ville-Pekka Vainio