Merge with MySQL 5.1.55

- Fixed some issues with partitions and connection_string, which also fixed lp:716890 "Pre- and post-recovery crash in Aria"
- Fixed wrong assert in Aria

Now need to merge with latest xtradb before pushing 

sql/ha_partition.cc:
  Ensure that m_ordered_rec_buffer is not freed before close.
sql/mysqld.cc:
  Changed to use opt_stack_trace instead of opt_pstack.
  Removed references to pstack
sql/partition_element.h:
  Ensure that connect_string is initialized
storage/maria/ma_key_recover.c:
  Fixed wrong assert

dbug/dbug.c

@@ -2446,6 +2446,25 @@ void _db_flush_()
 }
 
 
+#ifndef __WIN__
+void _db_suicide_()
+{
+  int retval;
+  sigset_t new_mask;
+  sigfillset(&new_mask);
+
+  fprintf(stderr, "SIGKILL myself\n");
+  fflush(stderr);
+
+  retval= kill(getpid(), SIGKILL);
+  assert(retval == 0);
+  retval= sigsuspend(&new_mask);
+  fprintf(stderr, "sigsuspend returned %d errno %d \n", retval, errno);
+  assert(FALSE); /* With full signal mask, we should never return here. */
+}
+#endif  /* ! __WIN__ */
+
+
 void _db_lock_file_()
 {
   CODE_STATE *cs;