It appears that make_scrambled_password has been deprecated for some time and
has gone away in MySQL 5.5 on Fedora, though not upstream, in favour of
my_make_scrambled_password.

http://bugs.proftpd.org/3669
http://bugzilla.redhat.com/718327

--- proftpd-1.3.4rc3/contrib/mod_sql_mysql.c
+++ proftpd-1.3.4rc3/contrib/mod_sql_mysql.c
@@ -1477,8 +1477,14 @@
 
 #if MYSQL_VERSION_ID >= 40100 && MYSQL_VERSION_ID < 40101
   make_scrambled_password(scrambled, c_clear, 1, NULL);
-#else
+#elif MYSQL_VERSION_ID >= 40101 && MYSQL_VERSION_ID < 50501
   make_scrambled_password(scrambled, c_clear);
+#else
+  /* Fedora 15 has removed the long-deprecated make_scrambled_password
+   * symbol, so use the preferred my_make_scrambled_password routine
+   * instead.
+   */
+  my_make_scrambled_password(scrambled, c_clear, strlen(c_clear));
 #endif
 
   success = !strcmp(scrambled, c_hash);