Transition to NEWUNIT option for unique file unit

[scrasmussen]

Transition to NEWUNIT option for unique file unit

ICAR currently calls the subroutine io_newunit from io/io_routines.f90 to get a unique file unit. There is a new open option to make sure a file is opened with a unique identifier, e.g. open(newunit=unit,file='foo.txt'). I think it would be beneficial to offload that behavior to the compiler implementation.

[gutmann]

In general I like the idea, but this was only recently added to some compilers, so requiring it might hurt people running older systems, while not providing any significant benefit that I can see. Are there reasons this is better? Speed isn't really a concern, the current code has been used a long time and has been robust across compilers / systems, the code doesn't add spaghetti.

If it ain't broke don't fix it?