python-paramiko: Add patch for ECDSA private keys.

This patch should be backwards-incompatible and is also submitted
upstream as paramiko/paramiko#218.

The main reason for this patch is that we need it for NixOS/nixops#124
in order to cope with NixOS/nixops@a2718b6, which makes ECDSA private
key the default for new deployments.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>