Merge pull request #3 from johntconklin/master

Cherry-picked configure and rpmbuild fixes from libzmq/master
Fix issue #1224
Backported pull request #1225
Merge pull request #4 from hintjens/master

Backported fixes from master
Add --with-libgssapi_krb5 to match libsodium and pgm.
Add support for --with/--without libgssapi_krb5
Pass --with/--without-libgssapi_krb5 to configure.
Correct libgssapi_krb5 packages.