Introduced a leak of disk_log processes in the rewrite to try-catch.

There is no need to update the index table if a record is updated in non
indexed field. This removes one timing glitch where dirty_index_read would
return an empty list for records that where updated.

There is still an issue with dirty_index_read when updates are made to
the index field, it have been reduced but the real table updates are made
after the index table references have been added.

Originally reported by Nick Marino in erl-questions mailing list, thanks.

The docs express that exit({aborted, Reason}) are called when
an error occur.

* dgud/mnesia/try-catch:
  mnesia: Replace catch with try-catch

Avoids building stacktraces where it is not needed and do
not mask errors, i.e. only catch the relevant classes in each try.