The equity:conversion account, and its variations equity:trade(s) and equity:trading,
normally detected as V/Conversion type, now become ordinary E/Equity accounts
if some other account is declared as V/Conversion type.
This is motivated by the next commit, in which `check accounts` will
stop warning about conversion accounts and their subaccounts,
which means all of the above names and their subaccounts would remain
always exempt from strict account checking.
Now, if the user declares their own conversion account, those default
accounts will become controllable by account checking again.
Which at least reduces the allowlist a bit.
Hopefully this won't cause hassles.
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