Added references to the appropriate RFC.

Rev: src/nettle/testsuite/md2-test.c:1.2
Rev: src/nettle/testsuite/md4-test.c:1.2

testsuite/md2-test.c

@@ -4,6 +4,7 @@
 int
 test_main(void)
 {
+  /* Testcases from RFC 1319 */
   test_hash(&nettle_md2, 0, "",
 	    H("8350e5a3e24c153df2275c9f80692773"));
   test_hash(&nettle_md2, LDATA("a"),

testsuite/md4-test.c

@@ -4,6 +4,7 @@
 int
 test_main(void)
 {
+  /* Testcases from RFC 1320 */
   test_hash(&nettle_md4, LDATA(""),
 	    H("31d6cfe0d16ae931b73c59d7e0c089c0"));
   test_hash(&nettle_md4, LDATA("a"),