Add test for EC keys with all curves.

(Made possible by the OID fix.)
diff --git a/tests/data_files/ec_521_pub.pem b/tests/data_files/ec_521_pub.pem
new file mode 100644
index 0000000..26bc5c5
--- /dev/null
+++ b/tests/data_files/ec_521_pub.pem
@@ -0,0 +1,6 @@
+-----BEGIN PUBLIC KEY-----
+MIGbMBAGByqGSM49AgEGBSuBBAAjA4GGAAQAHeFC1U9p6wOO5LevnTygdzb9nPcZ
+6zVNaYee5/PBNvsPv58I+Gvl+hKOwaBR0+bGQ+ha2o/6zzZjwmC9LIRLb1YAzujk
+ip5l0Jyt2J8jXe4F87imRr5xXx9n1bQ04P8jofwH73dAGT5A7v9vO839dlqpFVAz
+Uk/k8gX1RE4pLEwvasE=
+-----END PUBLIC KEY-----