trio flag broken for pcaer

[rkwalters]

pcaer_20 reliably fails at step me300 when specifying --trio.

The cause of the error is that the trio flag defines a trio_ex_file to be used with as ie_file (at line 978-981) which is passed to bcomb at line 1088, but the code to create that file (line 1049-1054) has been commented out by the if(0) on the block starting line 1022.

Currently unclear to me whether the fix is to re-activate the code creating the trio_ex_file or to stop that argument from being passed to bcomb.