Fix assorted minor memory leaks.

All found by Coverity.

unix/uxagentsock.c

@@ -29,6 +29,7 @@ Socket *platform_make_agent_socket(
     if ((errw = make_dir_and_check_ours(socketdir)) != NULL) {
         *error = dupprintf("%s: %s\n", socketdir, errw);
         sfree(errw);
+        sfree(socketdir);
         return NULL;
     }
 

unix/uxsftp.c

@@ -490,6 +490,7 @@ static int ssh_sftp_do_select(bool include_stdin, bool no_fds_ok)
 
         if (i < 1 && !no_fds_ok && !toplevel_callback_pending()) {
             pollwrap_free(pw);
+            sfree(fdlist);
             return -1;                 /* doom */
         }