make circ->onionskin a pointer, not a static array. moria2 was using

125000 circuit_t's after it had been up for a few weeks, which translates
to 20+ megs of wasted space.


svn:r5333

src/or/command.c

@@ -200,6 +200,7 @@ command_process_create_cell(cell_t *cell, connection_t *conn)
   circ->purpose = CIRCUIT_PURPOSE_OR;
   circ->state = CIRCUIT_STATE_ONIONSKIN_PENDING;
   if (cell->command == CELL_CREATE) {
+    circ->onionskin = tor_malloc(ONIONSKIN_CHALLENGE_LEN);
     memcpy(circ->onionskin, cell->payload, ONIONSKIN_CHALLENGE_LEN);
 
     /* hand it off to the cpuworkers, and then return */