Fix a memleak

Found by coverity

test_mem_op_hex was leaking memory, which showed up in a few
tests.

Also, the dir_param test had a memleak of its own.

Found by Coverity

src/test/test.h

@@ -58,6 +58,7 @@
   tor_assert((length&1)==0);                                            \
   base16_decode(value2, length/2, hex, length);                         \
   test_mem_op(expr1, op, value2, length/2);                             \
+  tor_free(value2);                                                     \
   STMT_END
 
 #define test_memeq_hex(expr1, hex) test_mem_op_hex(expr1, ==, hex)

src/test/test_dir.c

@@ -504,6 +504,7 @@ test_dir_param_voting(void)
   smartlist_free(vote2.net_params);
   smartlist_free(vote3.net_params);
   smartlist_free(vote4.net_params);
+  smartlist_free(votes);
 
   return;
 }