|EVP_get_digestbyname| and |EVP_get_digestbynid|: recognize MD4.

This benefits nodejs.

Change-Id: I21bf7e64c2a44e96f27b427ad4bd44551c33221c
Reviewed-on: https://boringssl-review.googlesource.com/5721
Reviewed-by: Adam Langley <agl@google.com>

crypto/digest/digests.c

diff --git a/crypto/digest/digests.c b/crypto/digest/digests.c
index cdcc6f1..3307f26 100644
--- a/crypto/digest/digests.c
+++ b/crypto/digest/digests.c
@@ -262,6 +262,7 @@
 };
 
 static const struct nid_to_digest nid_to_digest_mapping[] = {
+  { NID_md4, EVP_md4, SN_md4, LN_md4 },
   { NID_md5, EVP_md5, SN_md5, LN_md5 },
   { NID_sha1, EVP_sha1, SN_sha1, LN_sha1 },
   { NID_sha224, EVP_sha224, SN_sha224, LN_sha224 },