#4400, #5462: Move SSHA1 helpers to crypto-utils

On a way to factoring out OpenSSL support to a standalone file to ease
addition of other crypto libraries support in the future, move helpers
providing SSHA1 password generation and checking to crypto-utils.{c,h}.

libtransmission/crypto-utils.h

@@ -154,6 +154,17 @@ int              tr_rand_int_weak      (int              upper_bound);
 bool             tr_rand_buffer        (void           * buffer,
                                         size_t           length);
 
+/**
+ * @brief Generate a SSHA password from its plaintext source.
+ */
+char           * tr_ssha1              (const char     * plain_text) TR_GNUC_MALLOC;
+
+/**
+ * @brief Validate a test password against the a ssha1 password.
+ */
+bool             tr_ssha1_matches      (const char     * ssha1,
+                                        const char     * plain_text);
+
 /**
  * @brief Translate a block of bytes into base64.
  * @return a newly-allocated null-terminated string that can be freed with tr_free ()