Add test for EC keys with all curves.

(Made possible by the OID fix.)
diff --git a/tests/data_files/ec_384_prv.pem b/tests/data_files/ec_384_prv.pem
new file mode 100644
index 0000000..7890759
--- /dev/null
+++ b/tests/data_files/ec_384_prv.pem
@@ -0,0 +1,6 @@
+-----BEGIN EC PRIVATE KEY-----
+MIGkAgEBBDA/XY2b4oC1aWzFzJ+Uz4r35rYd1lkrKrKzpMYHRQQX7DJ9zcrtfBAF
+PXGaBXTwp2qgBwYFK4EEACKhZANiAATZxmK1C6KcpHmQRQ4EOur08MabFWdtES9i
+KnHJMFmvmZaRxWgNK0TREVedsS9KQTou1cRfz7Z7W2PgC5Hr5Z0JprGsLAxCgqoS
+MX7VkU+Zm8SIuxMug0LMNvLKXjN5x0c=
+-----END EC PRIVATE KEY-----