checksums.openssl: make evp-md-context private.

basis/checksums/openssl/openssl.factor

@@ -17,6 +17,8 @@ INSTANCE: openssl-checksum stream-checksum
 
 C: <openssl-checksum> openssl-checksum
 
+<PRIVATE
+
 TUPLE: evp-md-context < disposable handle ;
 
 : <evp-md-context> ( -- ctx )
@@ -26,8 +28,6 @@ TUPLE: evp-md-context < disposable handle ;
 M: evp-md-context dispose*
     handle>> EVP_MD_CTX_destroy ;
 
-<PRIVATE
-
 : digest-named ( name -- md )
     dup EVP_get_digestbyname
     [ ] [ unknown-digest ] ?if ;