Provide support for enctype aliases for ease of use.

This should be compatible with MIT krb5 at least from my memory.

lib/krb5/crypto.h

@@ -103,6 +103,7 @@ struct _krb5_checksum_type {
 struct _krb5_encryption_type {
     krb5_enctype type;
     const char *name;
+    const char *alias;
     size_t blocksize;
     size_t padsize;
     size_t confoundersize;