Fix for broadcast_file for NAG compiler based on broadcast_string

[DJDavies2]

Description

Fix broadcast_file for NAG compiler by copying the solution for broadcast_string.

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[DJDavies2]

I don't know why the character handling is done differently in broadcast_string to broadcast_path, it seems to have been done a long time ago. It ought to be possible to write a function to do this. I guess that is what c_str is supposed to be? Maybe there is a problem with it.

[DJDavies2]

Looking at c_str, it doesn't do the same thing as the chunk of code in broadcast_string (and now broadcast_file). c_str just appends a c_null_char, I'm not sure why one couldn't just do that directly? The code chunk in broadcast_string converts a fortran string into an array of single character strings with a c_null_char appended, which is a very different thing.

[DJDavies2]

One calls fckit__mpi__broadcast_string, the other fckit__mpi__broadcast_file. However these have the same declaration for the string arguments (an assumed size array of len=1 characters of kind c_char). The code chunk matches that whereas c_str doesn't.

[DJDavies2]

Fix for #81

[wdeconinck]

Thanks for this fix. I see the problem now, and I have tried another fix in #89 which should hopefully also work and avoids the copies altogether, and should be more performant.