Context::importKeys: try the old export-external + import way of importing keys from an X.509 keyserver when import_key isn't available or indicates that gpgsm is too old. Unfortunately, we don't have such a fallback for OpenPGP, and we don't go the whole way and provide the same for startKeyImport(), since that would be too much work.

svn path=/branches/kdepim/enterprise4/kdepimlibs/; revision=985430