Avoid hanging waiting for other processes on other node
to commit.

Fixed a race where some parts of a transaction could
be added to the checkpoint.

There are probably more races here but this improves the current
testcases.

We don't support communicating with such old nodes anyway.

* nm/mnesia_idx_insert_speedup/OTP-11103:
  Fix missing case clause for ordered_set tables
  Optimize index creation for Mnesia set tables

The previous commit contained a regression that would trigger a crash
when attempting to add an index to an Mnesia table of type ordered_set.

ETS bag tables have very poor performance on insertion if you have lots
of rows with duplicate keys, since it has to check each existing record
and make sure it's not inserting any duplicates. This can lead to some
pretty drastic slowdowns when inserting lots of rows into an Mnesia
table, IF you're introducing lots of duplicate values into an indexed
column.

As it turns out, we can fix this by switching to duplicate_bag tables
for storing Mnesia indexes on tables of type 'set', and it ultimately
makes no functional difference since we will never actually attempt to
insert any duplicate records anyway. (We would have to make some bigger
changes to make this work for Mnesia bag tables though, so that is left
as a possible enhancement for the future.)

If mnesia:cleartable/1 was called during a table_load an schema event
with delete and write of that table is sent, which caused the table
to contain the schema record instead of clearing the table.